def validate(self, data):  
lms_user_id = data.get('<STR_LIT>')<EOL>tpa_user_id = data.get('<STR_LIT>')<EOL>user_email = data.get('<STR_LIT>')<EOL>if not lms_user_id and not tpa_user_id and not user_email:<EOL><INDENT>raise serializers.ValidationError(<EOL>'<STR_LIT>'<EOL>'<STR_LIT>'<EOL>)<EOL><DEDENT>return data<EOL>
Validate that at least one of the user identifier fields has been passed in.