Fix PyDoc: Invalid signature for functions without arguments

Ref: !130031

doc/python_api/sphinx_doc_gen.py

@@ -1893,7 +1893,7 @@ def pyrna2sphinx(basepath):
             for op in ops_mod:
                 args_str = ", ".join(prop.get_arg_default(force=True) for prop in op.args)
                 # All operator arguments are keyword only (denoted by the leading `*`).
-                fw(".. function:: {:s}(*, {:s})\n\n".format(op.func_name, args_str))
+                fw(".. function:: {:s}({:s}{:s})\n\n".format(op.func_name, "*, " if args_str else "", args_str))
 
                 # If the description isn't valid, we output the standard warning
                 # with a link to the wiki so that people can help.