diff --git a/felt_python/api.py b/felt_python/api.py
index 68c91d1..73fbf2d 100644
--- a/felt_python/api.py
+++ b/felt_python/api.py
@@ -4,6 +4,7 @@
 import json as json_
 import os
 import typing
+import urllib.parse
 import urllib.request
 from importlib.metadata import version, PackageNotFoundError
 
@@ -20,6 +21,36 @@
 BASE_URL = os.getenv("FELT_BASE_URL", "https://felt.com/api/v2/")
 
 
+def build_url(template: str, **path_params) -> str:
+    """Fill a URL template, percent-encoding each value as one path segment.
+
+    Ids reach these functions from user code, config files and other API
+    responses, so they cannot be assumed URL-safe. Interpolating them directly
+    means an id containing a space raises http.client.InvalidURL before the
+    request is sent, and one containing "?", "#" or "/" silently changes the
+    path or query the server sees. Encoding each value with safe="" keeps a
+    bad id a plain 404.
+
+        >>> build_url(BASE_URL + "maps/{map_id}", map_id="a b/c")
+        'https://felt.com/api/v2/maps/a%20b%2Fc'
+    """
+    return template.format(
+        **{
+            key: urllib.parse.quote(str(value), safe="")
+            for key, value in path_params.items()
+        }
+    )
+
+
+def build_query(url: str, **params) -> str:
+    """Append a percent-encoded query string, skipping None values."""
+    present = {key: value for key, value in params.items() if value is not None}
+    if not present:
+        return url
+    separator = "&" if "?" in url else "?"
+    return f"{url}{separator}{urllib.parse.urlencode(present)}"
+
+
 def make_request(
     url: str,
     method: typing.Literal["GET", "POST", "PATCH", "DELETE"],
diff --git a/felt_python/comments.py b/felt_python/comments.py
index 9152b2d..94f8aa5 100644
--- a/felt_python/comments.py
+++ b/felt_python/comments.py
@@ -4,7 +4,7 @@
 
 from urllib.parse import urljoin
 
-from .api import make_request, BASE_URL
+from .api import BASE_URL, build_query, build_url, make_request
 
 
 COMMENT = urljoin(BASE_URL, "maps/{map_id}/comments/{comment_id}")
@@ -23,7 +23,7 @@ def export_comments(map_id: str, format: str = "json", api_token: str | None = N
     Returns:
         The exported comments in the specified format
     """
-    url = f"{COMMENT_EXPORT.format(map_id=map_id)}?format={format}"
+    url = build_query(build_url(COMMENT_EXPORT, map_id=map_id), format=format)
     response = make_request(
         url=url,
         method="GET",
@@ -44,7 +44,7 @@ def resolve_comment(map_id: str, comment_id: str, api_token: str | None = None):
         Confirmation of the resolved comment
     """
     response = make_request(
-        url=COMMENT_RESOLVE.format(map_id=map_id, comment_id=comment_id),
+        url=build_url(COMMENT_RESOLVE, map_id=map_id, comment_id=comment_id),
         method="POST",
         api_token=api_token,
     )
@@ -60,7 +60,7 @@ def delete_comment(map_id: str, comment_id: str, api_token: str | None = None):
         api_token: Optional API token
     """
     make_request(
-        url=COMMENT.format(map_id=map_id, comment_id=comment_id),
+        url=build_url(COMMENT, map_id=map_id, comment_id=comment_id),
         method="DELETE",
         api_token=api_token,
     )
diff --git a/felt_python/elements.py b/felt_python/elements.py
index fcd86dd..cacfb58 100644
--- a/felt_python/elements.py
+++ b/felt_python/elements.py
@@ -4,7 +4,7 @@
 
 from urllib.parse import urljoin
 
-from .api import make_request, BASE_URL
+from .api import BASE_URL, build_url, make_request
 from .util import deprecated
 
 
@@ -25,7 +25,7 @@ def list_elements(map_id: str, api_token: str | None = None):
         GeoJSON FeatureCollection of all elements
     """
     response = make_request(
-        url=ELEMENTS.format(map_id=map_id),
+        url=build_url(ELEMENTS, map_id=map_id),
         method="GET",
         api_token=api_token,
     )
@@ -43,7 +43,7 @@ def list_element_groups(map_id: str, api_token: str | None = None):
         List of element groups
     """
     response = make_request(
-        url=ELEMENT_GROUPS.format(map_id=map_id),
+        url=build_url(ELEMENT_GROUPS, map_id=map_id),
         method="GET",
         api_token=api_token,
     )
@@ -62,7 +62,7 @@ def get_element_group(map_id: str, element_group_id: str, api_token: str | None
         GeoJSON FeatureCollection of all elements in the group
     """
     response = make_request(
-        url=ELEMENT_GROUP.format(map_id=map_id, element_group_id=element_group_id),
+        url=build_url(ELEMENT_GROUP, map_id=map_id, element_group_id=element_group_id),
         method="GET",
         api_token=api_token,
     )
@@ -106,7 +106,7 @@ def upsert_elements(
             "geojson_feature_collection must be a valid GeoJSON"
         )
     response = make_request(
-        url=ELEMENTS.format(map_id=map_id),
+        url=build_url(ELEMENTS, map_id=map_id),
         method="POST",
         json=geojson_feature_collection,
         api_token=api_token,
@@ -123,7 +123,7 @@ def delete_element(map_id: str, element_id: str, api_token: str | None = None):
         api_token: Optional API token
     """
     make_request(
-        url=ELEMENT.format(map_id=map_id, element_id=element_id),
+        url=build_url(ELEMENT, map_id=map_id, element_id=element_id),
         method="DELETE",
         api_token=api_token,
     )
@@ -159,7 +159,7 @@ def upsert_element_groups(
         The created or updated element groups
     """
     response = make_request(
-        url=ELEMENT_GROUPS.format(map_id=map_id),
+        url=build_url(ELEMENT_GROUPS, map_id=map_id),
         method="POST",
         json=element_groups,
         api_token=api_token,
diff --git a/felt_python/layer_groups.py b/felt_python/layer_groups.py
index 4dfdbfc..851f3fc 100644
--- a/felt_python/layer_groups.py
+++ b/felt_python/layer_groups.py
@@ -4,7 +4,7 @@
 
 from urllib.parse import urljoin
 
-from .api import make_request, BASE_URL
+from .api import BASE_URL, build_url, make_request
 
 
 GROUPS = urljoin(BASE_URL, "maps/{map_id}/layer_groups")
@@ -25,7 +25,7 @@ def list_layer_groups(map_id: str, api_token: str | None = None):
         List of layer groups
     """
     response = make_request(
-        url=GROUPS.format(map_id=map_id),
+        url=build_url(GROUPS, map_id=map_id),
         method="GET",
         api_token=api_token,
     )
@@ -48,7 +48,7 @@ def get_layer_group(
         Layer group details
     """
     response = make_request(
-        url=GROUP.format(map_id=map_id, layer_group_id=layer_group_id),
+        url=build_url(GROUP, map_id=map_id, layer_group_id=layer_group_id),
         method="GET",
         api_token=api_token,
     )
@@ -73,7 +73,7 @@ def update_layer_groups(
         The updated layer groups
     """
     response = make_request(
-        url=GROUPS.format(map_id=map_id),
+        url=build_url(GROUPS, map_id=map_id),
         method="POST",
         json=layer_group_params_list,
         api_token=api_token,
@@ -94,7 +94,7 @@ def delete_layer_group(
         api_token: Optional API token
     """
     make_request(
-        url=GROUP.format(map_id=map_id, layer_group_id=layer_group_id),
+        url=build_url(GROUP, map_id=map_id, layer_group_id=layer_group_id),
         method="DELETE",
         api_token=api_token,
     )
@@ -136,7 +136,7 @@ def update_layer_group(
         json_payload["visibility_interaction"] = visibility_interaction
 
     response = make_request(
-        url=GROUP.format(map_id=map_id, layer_group_id=layer_group_id),
+        url=build_url(GROUP, map_id=map_id, layer_group_id=layer_group_id),
         method="POST",
         json=json_payload,
         api_token=api_token,
@@ -166,7 +166,7 @@ def publish_layer_group(
         json_payload["name"] = name
 
     response = make_request(
-        url=GROUPS_PUBLISH.format(map_id=map_id, layer_group_id=layer_group_id),
+        url=build_url(GROUPS_PUBLISH, map_id=map_id, layer_group_id=layer_group_id),
         method="POST",
         json=json_payload,
         api_token=api_token,
diff --git a/felt_python/layers.py b/felt_python/layers.py
index 35f6d02..ff969cc 100644
--- a/felt_python/layers.py
+++ b/felt_python/layers.py
@@ -10,7 +10,7 @@
 
 from urllib.parse import urljoin
 
-from .api import make_request, BASE_URL
+from .api import BASE_URL, build_url, make_request
 from .util import deprecated
 
 
@@ -31,7 +31,7 @@
 def list_layers(map_id: str, api_token: str | None = None):
     """List layers on a map"""
     response = make_request(
-        url=LAYERS.format(map_id=map_id),
+        url=build_url(LAYERS, map_id=map_id),
         method="GET",
         api_token=api_token,
     )
@@ -79,7 +79,7 @@ def upload_file(
         json_payload["zoom"] = zoom
 
     response = make_request(
-        url=LAYER_UPLOAD.format(map_id=map_id),
+        url=build_url(LAYER_UPLOAD, map_id=map_id),
         method="POST",
         api_token=api_token,
         json=json_payload,
@@ -147,7 +147,7 @@ def refresh_file_layer(
         The refresh response including presigned upload details
     """
     response = make_request(
-        url=LAYER_REFRESH.format(map_id=map_id, layer_id=layer_id),
+        url=build_url(LAYER_REFRESH, map_id=map_id, layer_id=layer_id),
         method="POST",
         api_token=api_token,
     )
@@ -186,7 +186,7 @@ def upload_url(
         json_payload["hints"] = hints
 
     response = make_request(
-        url=LAYER_UPLOAD.format(map_id=map_id),
+        url=build_url(LAYER_UPLOAD, map_id=map_id),
         method="POST",
         api_token=api_token,
         json=json_payload,
@@ -197,7 +197,8 @@ def upload_url(
 def refresh_url_layer(map_id: str, layer_id: str, api_token: str | None = None):
     """Refresh a layer originated from a URL upload"""
     response = make_request(
-        url=LAYER_REFRESH.format(
+        url=build_url(
+            LAYER_REFRESH,
             map_id=map_id,
             layer_id=layer_id,
         ),
@@ -219,7 +220,8 @@ def get_layer(
 ):
     """Get details of a layer"""
     response = make_request(
-        url=LAYER.format(
+        url=build_url(
+            LAYER,
             map_id=map_id,
             layer_id=layer_id,
         ),
@@ -237,7 +239,8 @@ def update_layer_style(
 ):
     """Update a layer's style"""
     response = make_request(
-        url=LAYER_UPDATE_STYLE.format(
+        url=build_url(
+            LAYER_UPDATE_STYLE,
             map_id=map_id,
             layer_id=layer_id,
         ),
@@ -258,7 +261,7 @@ def get_export_link(
     Vector layers will be downloaded in GPKG format. Raster layers will be GeoTIFFs.
     """
     response = make_request(
-        url=LAYER_EXPORT_LINK.format(map_id=map_id, layer_id=layer_id),
+        url=build_url(LAYER_EXPORT_LINK, map_id=map_id, layer_id=layer_id),
         method="GET",
         api_token=api_token,
     )
@@ -306,7 +309,7 @@ def update_layers(
         The updated layers
     """
     response = make_request(
-        url=LAYERS.format(map_id=map_id),
+        url=build_url(LAYERS, map_id=map_id),
         method="POST",
         json=layer_params_list,
         api_token=api_token,
@@ -321,7 +324,7 @@ def delete_layer(
 ):
     """Delete a layer from a map"""
     make_request(
-        url=LAYER.format(map_id=map_id, layer_id=layer_id),
+        url=build_url(LAYER, map_id=map_id, layer_id=layer_id),
         method="DELETE",
         api_token=api_token,
     )
@@ -349,7 +352,7 @@ def publish_layer(
         json_payload["name"] = name
 
     response = make_request(
-        url=LAYER_PUBLISH.format(map_id=map_id, layer_id=layer_id),
+        url=build_url(LAYER_PUBLISH, map_id=map_id, layer_id=layer_id),
         method="POST",
         json=json_payload,
         api_token=api_token,
@@ -389,7 +392,7 @@ def create_custom_export(
         json_payload["filters"] = filters
 
     response = make_request(
-        url=LAYER_CUSTOM_EXPORT.format(map_id=map_id, layer_id=layer_id),
+        url=build_url(LAYER_CUSTOM_EXPORT, map_id=map_id, layer_id=layer_id),
         method="POST",
         json=json_payload,
         api_token=api_token,
@@ -415,7 +418,8 @@ def get_custom_export_status(
         Export status including download URL when complete
     """
     response = make_request(
-        url=LAYER_CUSTOM_EXPORT_STATUS.format(
+        url=build_url(
+            LAYER_CUSTOM_EXPORT_STATUS,
             map_id=map_id,
             layer_id=layer_id,
             export_id=export_id,
diff --git a/felt_python/library.py b/felt_python/library.py
index 26aa0b9..839f666 100644
--- a/felt_python/library.py
+++ b/felt_python/library.py
@@ -4,7 +4,7 @@
 
 from urllib.parse import urljoin
 
-from .api import make_request, BASE_URL
+from .api import BASE_URL, build_query, make_request
 
 
 LIBRARY = urljoin(BASE_URL, "library")
@@ -24,7 +24,7 @@ def list_library_layers(source: str = "workspace", api_token: str | None = None)
     Returns:
         The layer library containing layers and layer groups
     """
-    url = f"{LIBRARY}?source={source}"
+    url = build_query(LIBRARY, source=source)
     response = make_request(
         url=url,
         method="GET",
diff --git a/felt_python/maps.py b/felt_python/maps.py
index 904a10f..5af3a55 100644
--- a/felt_python/maps.py
+++ b/felt_python/maps.py
@@ -4,7 +4,7 @@
 
 from urllib.parse import urljoin
 
-from .api import make_request, BASE_URL
+from .api import BASE_URL, build_query, build_url, make_request
 from .util import deprecated
 
 
@@ -89,7 +89,7 @@ def create_map(
 def delete_map(map_id: str, api_token: str | None = None):
     """Delete a map"""
     make_request(
-        url=MAP.format(map_id=map_id),
+        url=build_url(MAP, map_id=map_id),
         method="DELETE",
         api_token=api_token,
     )
@@ -98,7 +98,7 @@ def delete_map(map_id: str, api_token: str | None = None):
 def get_map(map_id: str, api_token: str | None = None):
     """Get details of a map"""
     response = make_request(
-        url=MAP.format(map_id=map_id),
+        url=build_url(MAP, map_id=map_id),
         method="GET",
         api_token=api_token,
     )
@@ -162,7 +162,7 @@ def update_map(
         json_args["viewer_permissions"] = viewer_permissions
 
     response = make_request(
-        url=MAP_UPDATE.format(map_id=map_id),
+        url=build_url(MAP_UPDATE, map_id=map_id),
         method="POST",
         json=json_args,
         api_token=api_token,
@@ -199,7 +199,7 @@ def move_map(
         json_args["folder_id"] = folder_id
 
     response = make_request(
-        url=MAP_MOVE.format(map_id=map_id),
+        url=build_url(MAP_MOVE, map_id=map_id),
         method="POST",
         json=json_args,
         api_token=api_token,
@@ -222,9 +222,7 @@ def create_embed_token(
     Returns:
         The created embed token with expiration time
     """
-    url = MAP_EMBED_TOKEN.format(map_id=map_id)
-    if user_email:
-        url = f"{url}?user_email={user_email}"
+    url = build_query(build_url(MAP_EMBED_TOKEN, map_id=map_id), user_email=user_email)
 
     response = make_request(
         url=url,
@@ -252,7 +250,7 @@ def add_source_layer(
         Acceptance status and links to the created resources
     """
     response = make_request(
-        url=MAP_ADD_SOURCE_LAYER.format(map_id=map_id),
+        url=build_url(MAP_ADD_SOURCE_LAYER, map_id=map_id),
         method="POST",
         json=source_layer_params,
         api_token=api_token,
@@ -294,7 +292,7 @@ def duplicate_map(
         json_args["destination"] = {"folder_id": folder_id}
 
     response = make_request(
-        url=MAP_DUPLICATE.format(map_id=map_id),
+        url=build_url(MAP_DUPLICATE, map_id=map_id),
         method="POST",
         json=json_args,
         api_token=api_token,
diff --git a/felt_python/projects.py b/felt_python/projects.py
index 6285197..34f5e04 100644
--- a/felt_python/projects.py
+++ b/felt_python/projects.py
@@ -4,7 +4,7 @@
 
 from urllib.parse import urljoin
 
-from .api import make_request, BASE_URL
+from .api import BASE_URL, build_query, build_url, make_request
 
 
 PROJECTS = urljoin(BASE_URL, "projects/")
@@ -14,9 +14,7 @@
 
 def list_projects(workspace_id: str | None = None, api_token: str | None = None):
     """List all projects accessible to the authenticated user"""
-    url = PROJECTS
-    if workspace_id:
-        url = f"{url}?workspace_id={workspace_id}"
+    url = build_query(PROJECTS, workspace_id=workspace_id)
     response = make_request(
         url=url,
         method="GET",
@@ -49,7 +47,7 @@ def create_project(name: str, visibility: str, api_token: str | None = None):
 def get_project(project_id: str, api_token: str | None = None):
     """Get details of a project"""
     response = make_request(
-        url=PROJECT.format(project_id=project_id),
+        url=build_url(PROJECT, project_id=project_id),
         method="GET",
         api_token=api_token,
     )
@@ -80,7 +78,7 @@ def update_project(
         json_args["visibility"] = visibility
 
     response = make_request(
-        url=PROJECT_UPDATE.format(project_id=project_id),
+        url=build_url(PROJECT_UPDATE, project_id=project_id),
         method="POST",
         json=json_args,
         api_token=api_token,
@@ -94,7 +92,7 @@ def delete_project(project_id: str, api_token: str | None = None):
     Note: This will delete all Folders and Maps inside the project!
     """
     make_request(
-        url=PROJECT.format(project_id=project_id),
+        url=build_url(PROJECT, project_id=project_id),
         method="DELETE",
         api_token=api_token,
     )
diff --git a/felt_python/sources.py b/felt_python/sources.py
index 1317b7e..90433f5 100644
--- a/felt_python/sources.py
+++ b/felt_python/sources.py
@@ -4,7 +4,7 @@
 
 from urllib.parse import urljoin
 
-from .api import make_request, BASE_URL
+from .api import BASE_URL, build_query, build_url, make_request
 
 
 SOURCES = urljoin(BASE_URL, "sources")
@@ -15,9 +15,7 @@
 
 def list_sources(workspace_id: str | None = None, api_token: str | None = None):
     """List all sources accessible to the authenticated user"""
-    url = SOURCES
-    if workspace_id:
-        url = f"{url}?workspace_id={workspace_id}"
+    url = build_query(SOURCES, workspace_id=workspace_id)
     response = make_request(
         url=url,
         method="GET",
@@ -59,7 +57,7 @@ def create_source(
 def get_source(source_id: str, api_token: str | None = None):
     """Get details of a source"""
     response = make_request(
-        url=SOURCE.format(source_id=source_id),
+        url=build_url(SOURCE, source_id=source_id),
         method="GET",
         api_token=api_token,
     )
@@ -94,7 +92,7 @@ def update_source(
         json_payload["permissions"] = permissions
 
     response = make_request(
-        url=SOURCE_UPDATE.format(source_id=source_id),
+        url=build_url(SOURCE_UPDATE, source_id=source_id),
         method="POST",
         json=json_payload,
         api_token=api_token,
@@ -105,7 +103,7 @@ def update_source(
 def delete_source(source_id: str, api_token: str | None = None):
     """Delete a source"""
     make_request(
-        url=SOURCE.format(source_id=source_id),
+        url=build_url(SOURCE, source_id=source_id),
         method="DELETE",
         api_token=api_token,
     )
@@ -118,7 +116,7 @@ def sync_source(source_id: str, api_token: str | None = None):
         The source reference with synchronization status
     """
     response = make_request(
-        url=SOURCE_SYNC.format(source_id=source_id),
+        url=build_url(SOURCE_SYNC, source_id=source_id),
         method="POST",
         api_token=api_token,
     )
diff --git a/tests/tests.py b/tests/tests.py
index d258d91..facc78b 100644
--- a/tests/tests.py
+++ b/tests/tests.py
@@ -17,6 +17,7 @@
 from projects_test import FeltProjectsTest
 from sources_test import FeltSourcesTest
 from delete_test import FeltDeleteTest
+from url_building_test import BuildQueryTest, BuildUrlTest
 
 
 if __name__ == "__main__":
@@ -32,6 +33,8 @@
 
     # Add all test classes
     test_cases = [
+        BuildUrlTest,
+        BuildQueryTest,
         FeltAPITest,
         FeltElementsTest,
         FeltLayersTest,
diff --git a/tests/url_building_test.py b/tests/url_building_test.py
new file mode 100644
index 0000000..7e02813
--- /dev/null
+++ b/tests/url_building_test.py
@@ -0,0 +1,99 @@
+"""
+Unit tests for URL construction.
+
+Unlike the rest of the suite these need no API token and make no requests.
+"""
+
+import os
+import sys
+import unittest
+
+sys.path.append(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from felt_python.api import build_query, build_url
+from felt_python.comments import COMMENT
+from felt_python.layers import LAYER
+from felt_python.maps import MAP
+
+
+class BuildUrlTest(unittest.TestCase):
+    def test_ordinary_ids_are_untouched(self):
+        """Felt's short slugs and UUIDs contain nothing that needs encoding."""
+        for map_id in (
+            "PF0ve5FaSWujSB5402D8wD",
+            "deadbeef-0000-0000-0000-000000000000",
+        ):
+            with self.subTest(map_id=map_id):
+                self.assertTrue(
+                    build_url(MAP, map_id=map_id).endswith(f"/maps/{map_id}")
+                )
+
+    def test_space_is_encoded_instead_of_raising(self):
+        """Previously http.client raised InvalidURL before sending anything."""
+        self.assertTrue(
+            build_url(MAP, map_id="not a real id").endswith("/maps/not%20a%20real%20id")
+        )
+
+    def test_query_and_fragment_cannot_escape_the_path(self):
+        """An id with "?" or "#" used to silently truncate the path."""
+        self.assertTrue(build_url(MAP, map_id="abc?x=1").endswith("/maps/abc%3Fx%3D1"))
+        self.assertTrue(build_url(MAP, map_id="abc#frag").endswith("/maps/abc%23frag"))
+
+    def test_slash_cannot_add_path_segments(self):
+        """safe="" is the point: a "/" in an id must not become a separator."""
+        url = build_url(MAP, map_id="../../sources")
+        self.assertTrue(url.endswith("/maps/..%2F..%2Fsources"), url)
+
+    def test_each_segment_is_encoded_independently(self):
+        url = build_url(LAYER, map_id="a b", layer_id="c/d")
+        self.assertTrue(url.endswith("/maps/a%20b/layers/c%2Fd"), url)
+
+    def test_unicode_ids(self):
+        self.assertTrue(build_url(MAP, map_id="mapa-ñ").endswith("/maps/mapa-%C3%B1"))
+
+    def test_non_string_values_are_coerced(self):
+        self.assertTrue(build_url(MAP, map_id=123).endswith("/maps/123"))
+
+    def test_multi_segment_template(self):
+        url = build_url(COMMENT, map_id="m1", comment_id="c1")
+        self.assertTrue(url.endswith("/maps/m1/comments/c1"), url)
+
+
+class BuildQueryTest(unittest.TestCase):
+    def test_none_values_are_omitted(self):
+        self.assertEqual(
+            build_query("https://x/api", workspace_id=None), "https://x/api"
+        )
+
+    def test_single_param(self):
+        self.assertEqual(
+            build_query("https://x/api", workspace_id="w1"),
+            "https://x/api?workspace_id=w1",
+        )
+
+    def test_values_are_encoded(self):
+        """A "+" in an email would otherwise decode server-side as a space."""
+        self.assertEqual(
+            build_query("https://x/api", user_email="a+b@example.com"),
+            "https://x/api?user_email=a%2Bb%40example.com",
+        )
+
+    def test_ampersand_cannot_inject_a_parameter(self):
+        self.assertEqual(
+            build_query("https://x/api", source="felt&admin=true"),
+            "https://x/api?source=felt%26admin%3Dtrue",
+        )
+
+    def test_appends_to_an_existing_query_string(self):
+        self.assertEqual(
+            build_query("https://x/api?a=1", b="2"), "https://x/api?a=1&b=2"
+        )
+
+    def test_mixed_present_and_absent(self):
+        self.assertEqual(
+            build_query("https://x/api", a="1", b=None), "https://x/api?a=1"
+        )
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)