Jade,
maybe it's different because it's content_type__create_type, but at least the package developer guide seems to be setting name_method as null:
select content_type__create_type(
'mfp_note', -- content_type
'content_revision', -- supertype
'MFP Note', -- pretty_name,
'MFP Notes', -- pretty_plural
'mfp_notes', -- table_name
'note_id', -- id_column
null -- name_method
);