fix (#194)

Author: odashi

src/latexify/codegen/expression_codegen.py

@@ -105,7 +105,7 @@ def _generate_sum_prod(self, node: ast.Call) -> str | None:
         Returns:
             Generated LaTeX, or None if the node has unsupported syntax.
         """
-        if not isinstance(node.args[0], ast.GeneratorExp):
+        if not node.args or not isinstance(node.args[0], ast.GeneratorExp):
             return None
 
         name = ast_utils.extract_function_name_or_none(node)

src/latexify/codegen/expression_codegen_test.py

@@ -221,6 +221,8 @@ def test_visit_call(code: str, latex: str) -> None:
 @pytest.mark.parametrize(
     "src_suffix,dest_suffix",
     [
+        # No arguments
+        ("()", r" \mathopen{}\left( \mathclose{}\right)"),
         # No comprehension
         ("(x)", r" x"),
         (