Fix empty class generation

When generating a client for a schema that includes empty types, etc, add
pass to the body.

Author: Ryan Nowakowski

ariadne_codegen/codegen.py

@@ -117,7 +117,7 @@ def generate_class_def(
     bases = cast(
         List[ast.expr], [ast.Name(id=name) for name in base_names] if base_names else []
     )
-    body = body if body else []
+    body = body if body else [ast.Pass()]
     if description:
         docstring = ast.Expr(value=ast.Constant(value=description))
         body.insert(0, docstring)

tests/codegen/test_generated_classes.py

@@ -38,3 +38,14 @@ def test_generate_class_def_with_description_adds_docstring():
     assert isinstance(docstring, ast.Expr)
     assert isinstance(docstring.value, ast.Constant)
     assert docstring.value.value == description
+
+
+def test_generate_class_def_with_empty_body_adds_pass():
+    name = "Xyz"
+
+    result = generate_class_def(name)
+
+    assert isinstance(result, ast.ClassDef)
+    assert result.name == name
+    pass_obj = result.body[0]
+    assert isinstance(pass_obj, ast.Pass)