Comment 1 for bug 881839

Hello,

This error usually comes under following circumstances:
1. There exists a calendar(working time) linked to Selected project for scheduling.
2. The working time has no working schedule defined(no o2m records).
3. OR The O2M field contains a record with NO day of the week defined.

There seems 3 possible ways to get rid of this situation.
A. Undoubtedly, the day of the week should be made mandatory.(I have no exceptional case as of now where we never need it defined).
B. Prompting the user to realize the configuration error.
C. If neither of the solutions can go as accepted, we can assign _defaults value.(We observed that the field is selection and no default is set, which is special mistake in itself). Still, GTK will have no issues, but web is subjected to throw error because web always adds a blank '' option to selection fields.

Attached branches contains the solutions.

Thanks,
Serpent Consulting Services.