User should not be able to remove RB's start date, End date or both once created.

[sandhiyakavi]

Description:
User should not be able to remove(make null) RB's start date, End date or both once created.

Steps to Reproduce:

1. Create RB with both start date and End date.
2. Check WP created for the same.
3. Edit the RB by removing both start and End date.
4. Check WP again.

Actual result:
WP still existed with old start and End date limit.

Expected result:
User should not be able to remove/make null the start date, End date or both

[sandhiyakavi]

verified the issue using topcoder-platform/taas-apis#202