:returns: If the database contains a message with the given
filename, then a class:`Message:` is returned. This
function returns None in the following situations:
* No message is found with the given filename
* An out-of-memory situation occurs
:returns: If the database contains a message with the given
filename, then a class:`Message:` is returned. This
function returns None in the following situations:
* No message is found with the given filename
* An out-of-memory situation occurs