show create table returns incorrect type for varchar

[smacker]

In gitbase we have for example refs table. In which column commit_hash is a VARCHAR(40) which was implemented here: src-d/gitbase#916

But the query

show create table refs

returns

CREATE TABLE `refs` (
  `repository_id` TEXT NOT NULL,
  `ref_name` TEXT NOT NULL,
  `commit_hash` VARCHAR NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4

I'm not sure if it's against mysql spec but at least sqlachemy fails to parse such schema with an error:

sqlalchemy.exc.CompileError: VARCHAR requires a length on dialect mysql