Updated: Comment #0
I'm aware that it was me who just recently introduced this, but yeah. Sorry...
There was a lot of copy-pasting involved in that issue, apparently a little bit too much...
Problem/Motivation
StringLong specifies a default value for a 'text' schema type.
'text' schema types do not support specifying a default value.
Proposed resolution
Remove the default value from the schema.
I also removed the 'not null'. Both 'not null' and 'default' are terribly inconsistent right now in core, especially between field items and hook_schema(). I'll open an issue for that.