How to use functions properly Robotframework IMAP library

this is my first post (not native English) :)

I would like to use "Get Multipart Field Names". This function has a return value, but I can not give an argument which email (index) should be used. The documentation has few information without a proper example. I tried many things. But I think this is my closest attempt: @{fields} Get Multipart Field Names

I always get the error: Suspended due to logged failure: AttributeError: 'NoneType' object has no attribute 'keys'

This is the function

    def get_multipart_field_names(self):
        """Returns all available header field names of selected multipart email message.

        Examples:
        | Get Multipart Field Names |
        """
        return list(self._mp_msg.keys())

When I hover over "keys()" it says: "(function) keys: Any"

I just want to have the encoded email body, so I can decrypt some words of it myself.

Probably keyword walk Multipart Email was not called prior to Get Multipart Field Names.

The probable order of keywords for your case could be :

1. Open Mailbox ...
2. ${mail_index} = wait for email ... - searching for email by status/subject etc
3. walk Multipart Email ${mail_index} - creating some internal objects being necessary for other multipart keywords!
4. ${field_names} = Get Multipart Field Names - should work now.