[generator] Fix an NRE when cloning a method with generic arguments (#1089)

Context: #1080
Context: 9e0a469
When building an updated
`com.google.firebase.firebase-components.csproj` in
xamarin/GooglePlayServicesComponents using a *post*- 9e0a469
`generator`, the build hits an NullReferenceException when attempting
to `Method.Clone (…)` a method with generic arguments:
error BG0000: System.NullReferenceException: Object reference not set to an instance of an object.
at MonoDroid.Generation.Method.Clone(GenBase declaringType) in C:\code\xamarin-android\external\Java.Interop\tools\generator\Java.Interop.Tools.Generator.ObjectModel\Method.cs:line 131
at MonoDroid.Generation.Method.Clone(GenBase declaringType) in C:\code\xamarin-android\external\Java.Interop\tools\generator\Java.Interop.Tools.Generator.ObjectModel\Method.cs:line 131
at MonoDroid.Generation.ClassGen.FixupAccessModifiers(CodeGenerationOptions opt) in C:\code\xamarin-android\external\Java.Interop\tools\generator\Java.Interop.Tools.Generator.ObjectModel\ClassGen.cs:line 67
at MonoDroid.Generation.ClassGen.FixupAccessModifiers(CodeGenerationOptions opt) in C:\code\xamarin-android\external\Java.Interop\tools\generator\Java.Interop.Tools.Generator.ObjectModel\ClassGen.cs:line 67
at Xamarin.Android.Binder.CodeGenerator.Validate(List`1 gens, CodeGenerationOptions opt, CodeGeneratorContext context) in C:\code\xamarin-android\external\Java.Interop\tools\generator\CodeGenerator.cs:line 300
at Xamarin.Android.Binder.CodeGenerator.Validate(List`1 gens, CodeGenerationOptions opt, CodeGeneratorContext context) in C:\code\xamarin-android\external\Java.Interop\tools\generator\CodeGenerator.cs:line 300
at Xamarin.Android.Binder.CodeGenerator.Run(CodeGeneratorOptions options, DirectoryAssemblyResolver resolver) in C:\code\xamarin-android\external\Java.Interop\tools\generator\CodeGenerator.cs:line 208
at Xamarin.Android.Binder.CodeGenerator.Run(CodeGeneratorOptions options, DirectoryAssemblyResolver resolver) in C:\code\xamarin-android\external\Java.Interop\tools\generator\CodeGenerator.cs:line 208
at Xamarin.Android.Binder.CodeGenerator.Run(CodeGeneratorOptions options) in C:\code\xamarin-android\external\Java.Interop\tools\generator\CodeGenerator.cs:line 50
at Xamarin.Android.Binder.CodeGenerator.Run(CodeGeneratorOptions options) in C:\code\xamarin-android\external\Java.Interop\tools\generator\CodeGenerator.cs:line 50
at Xamarin.Android.Binder.CodeGenerator.Main(String[] args) in C:\code\xamarin-android\external\Java.Interop\tools\generator\CodeGenerator.cs:line 33
at Xamarin.Android.Binder.CodeGenerator.Main(String[] args) in C:\code\xamarin-android\external\Java.Interop\tools\generator\CodeGenerator.cs:line 33
This is because the `MethodBase.GenericArguments` collection is `null`
unless it has items. Thus we need to create it before populating it
with items in `Method.Clone(GenBase)`.

Author: jpobst

tests/generator-Tests/Unit-Tests/GenBaseTests.cs

@@ -91,6 +91,22 @@ public void TestEqualsMethodsWithOneParameter ()
 Assert.False(c.RequiresNew(m.Name,m));
 }
 
+[Test]
+publicvoidTestMethodClone_GenericArguments()
+{
+varc=SupportTypeBuilder.CreateClass("java.myClass",options);
+varm=SupportTypeBuilder.CreateMethod(c,"DoStuff",options);
+
+m.GenericArguments=newGenericParameterDefinitionList{
+newGenericParameterDefinition("T",null)
+};
+
+varclone=m.Clone(c);
+
+Assert.AreEqual(1,clone.GenericArguments.Count);
+Assert.AreEqual("T",clone.GenericArguments[0].Name);
+}
+
 voidTestParameterlessMethods(stringname)
 {
 varc=SupportTypeBuilder.CreateClass("java.myClass",options);

tools/generator/Java.Interop.Tools.Generator.ObjectModel/Method.cs

@@ -126,9 +126,13 @@ public Method Clone (GenBase declaringType)
 clone.SourceFile=SourceFile;
 clone.JavadocInfo=JavadocInfo;
 
-if(GenericArguments!=null)
+if(GenericArguments!=null){
+if(clone.GenericArgumentsisnull)
+clone.GenericArguments=newGenericParameterDefinitionList();
+
 foreach(vargainGenericArguments)
 clone.GenericArguments.Add(ga.Clone());
+}
 
 foreach(varpinParameters)
 clone.Parameters.Add(p.Clone());