Can save formula column with no formula

SmartClient_SNAPSHOT_v91d_2014-02-05_PowerEdition

The formula editor will allow a user to save without a formula after creating a valid formula and then editing it.

- Create a new formula
- Save without a formula
- Observe that an error message pops up
- Enter valid formula and save
- Edit the formula
- Clear the formula
- Click save
- Observe no error and the formula saves without a formula