Dot and svg diagrams fail to generate without useful error message

[barnettwilliam]

When trying to generate dot or svg diagrams either exporting to a file or via Sphinx the diagram generation fails with no meaningful error just that the dot process exited code 1.

Retrieving the diagrams generated dot text string, creating a file, and using dot command directly more meaningful errors are given e.g.
Error: HandleCommandStateMachine_original.dot: syntax error in line 25 near ','

the corresponding lines in the dot file, excerpt from line 23-27:

 subgraph cluster_handle { 
 label=<<b>Handle</b><br/><font point-size=”9”>entry / on_enter_handle</font>>; 
 style=”rounded, solid”; // ****** LINE 25
 cluster=true; 
 penwidth=2.0;

Unicode right double quotation marks U201D ” are used throughout, replacing these with straight quotation marks U0022 " dot completes successfully and correctly generates the svg file.

Strangely the errors only seem to only be raised at subgraph styles that have multiple properties like the one shown in this example.

OS: Debian 12 (bookworm)
dot: 2.43.0
python-statemachine: 3.2.1
pydot: 4.0.1
sphinx: 9.0.4
pyhton: 3.11.2

Thank you for this excellent library, the ability to generate diagrams and visualise state machines is particularly nice!