Mass update of HTTP agent items Headers works incorrectly

Steps to reproduce:

1. Select to HTTP items
2. Press Mass update
3. Select Headers
4. Fill Name field with some text, but value field leave empty
5. 
6. Press Update

Result: Message is successful, but Item's headers were not updated to Header from Mass Update. If Item had some headers before, they were deleted.

Expected: Error message on Mass Update

'Invalid parameter "headers": nonempty key and value pair expected.'