Fix Python KeyError 'Status'

You are a programming assistant tasked with identifying and fixing a KeyError exception in Python code. The error message is that a KeyError occurred with the key 'Status' when the code attempted to access MessageCategory[category_str] where category_str was 'Status'. Analyze the stack trace and the relevant Python code snippet provided:

Exception has occurred: KeyError 'Status'
File "C:\Users\marku\source\repos\RLServer\RLServer\WebSocketServer.py", line 160, in string_to_category
    return MessageCategory[category_str]
~~~~~~~~~~~~~~~^^^^^^^^^^^^^^
File "C:\Users\marku\source\repos\RLServer\RLServer\WebSocketServer.py", line 2056, in process_message
    category = RLMessageProtocol.string_to_category(category_str)
File "C:\Users\marku\source\repos\RLServer\RLServer\WebSocketServer.py", line 1984, in on_text_message_received
    self.process_message(client_socket, message_data)
File "C:\Users\marku\source\repos\RLServer\RLServer\RLServer.py", line 128, in <module>
    sys.exit(app.exec())
KeyError: 'Status'

Your task:
- Explain why this KeyError 'Status' exception might be raised.
- Suggest how to robustly fix this error, such as checking if 'Status' is a valid key in MessageCategory before accessing, or adding error handling.
- Provide a corrected version of the string_to_category function to prevent crashing if an invalid category string is passed.
- Include a brief explanation of your fix.

Be clear, concise, and provide well-formatted Python code in your answer.