Field 'file_hash' doesn't have a default value

Issue Summary

New file_hash field in wagtailimages Image model having issue with mysql database (v5.7) when uploading images through wagtail admin.

Steps to Reproduce

1. Install following version described in Technical Details
2. Try to upload an image.

After looking into wagtail source it seems like, this issue lies in field definition

file_hash = models.CharField(max_length=40, blank=True, editable=False)

Possibly MySQL strict mode is throwing error as no default value has been provided for file_hash

Technical details

• Python version: 3.6
• Django version: 2.0.8
• Wagtail version: 2.1.3
• MySQL version: 5.7

Stack trace

Traceback (most recent call last):
  File ".venv/lib/python3.6/site-packages/django/db/backends/utils.py", line 85, in _execute
    return self.cursor.execute(sql, params)
  File ".venv/lib/python3.6/site-packages/django/db/backends/mysql/base.py", line 71, in execute
    return self.cursor.execute(query, args)
  File ".venv/lib/python3.6/site-packages/MySQLdb/cursors.py", line 250, in execute
    self.errorhandler(self, exc, value)
  File ".venv/lib/python3.6/site-packages/MySQLdb/connections.py", line 50, in defaulterrorhandler
    raise errorvalue
  File ".venv/lib/python3.6/site-packages/MySQLdb/cursors.py", line 247, in execute
    res = self._query(query)
  File ".venv/lib/python3.6/site-packages/MySQLdb/cursors.py", line 412, in _query
    rowcount = self._do_query(q)
  File ".venv/lib/python3.6/site-packages/MySQLdb/cursors.py", line 375, in _do_query
    db.query(q)
  File ".venv/lib/python3.6/site-packages/MySQLdb/connections.py", line 276, in query
    _mysql.connection.query(self, query)
_mysql_exceptions.IntegrityError: (1364, "Field 'file_hash' doesn't have a default value")

Possible Solution

For now I have manually altered the database with a default value -

Alter table wagtailimages_image modify column file_hash varchar(40) not null default '';

Field declaration might be like following, so that either a default value is there or null is accepted

file_hash = models.CharField(max_length=40, blank=True, null=True, editable=False)

Or

file_hash = models.CharField(max_length=40, blank=True, default='', editable=False)

[tombola]

Also of note, If you have upgraded to/past 2.2, and you have any custom image models you will need to run makemigrations to add the file hash for the model.

[shimulch]

@gasman You were right. Somehow our pipenv lock file were changed. Which led to different version of wagtail when migrating between servers.

Sorry for not checking out that. Anyway, we love wagtail.