Improve inference of the "correct" package dir

Signed-off-by: Abrar Rahman Protyasha <[email protected]>

rosdoc2/verbs/build/builders/sphinx_builder.py

@@ -414,8 +414,9 @@ def build(self, *, doc_build_folder, output_staging_directory):
  package_xml_directory,
  package_list[package_list.index(self.build_context.package.name)])
  except ValueError:
- package_src_directory = ''
- if not package_src_directory:
+ package_src_directory = None
+
+ if not package_src_directory or not os.path.isdir(package_src_directory):
  raise RuntimeError('Could not locate source directory to invoke sphinx-apidoc in. '
  'If this is package does not have a standard Python package layout, '
  'please specify the Python source in `rosdoc2.yaml`.')