Update parameter_validation.py

Author: Charlie-Mindified

flask_parameter_validation/parameter_validation.py

@@ -23,7 +23,7 @@ def nested_func(**kwargs):
                     return {"error": "Could not parse JSON."}, 400
             request_inputs = {
                 Route: kwargs.copy(),
-                Json: json_input,
+                Json: json_input if 'json_input' in vars() else None,
                 Query: request.args.to_dict(),
                 Form: request.form.to_dict(),
                 File: request.files.to_dict()