IntIntervalField can get invalid values.

[tvuotila]

Following Intervals result in invalid or wrong field value when set to IntIntervalField:

• Interval: IntInterval(None) hyphenized form: - which is invalid value for IntInterval.from_string(' -')
• Interval IntInterval([None, -3]) hyphenized form - -3 which is invalid value for IntInterval.from_string(' - -3')
• Interval: IntInterval([None, 3]) hyphenized form - 3 which gives IntInterval('[-3, -3]')

Also, value " " results in IntInterval('[,]') although it is an empty value.

[tvuotila]

The problem seems to be that IntIntervalField thinks that int_interval.hyphenized and IntInterval.from_string are each other's inverse functions.

[kvesteri]

Good catch! Probably the best way to solve this would be to add from_hyphenized_string() classmethod to Interval class in intervals package.