No input validation in adding records

[Timothy Vincent N. Pinawin]

Summary
There is no input validation when leaving input fields empty.

Steps to Produce:

1. Go to Sales tab:
2. Click on Add
3. Click Add"

Expected Results:
There should be an input validation saying to type in the empty fields,

Actual Results:
There was no input validation stating to type in the empty fields.

See 04-CSHAddSales, Iteration 1-2 and 1-3 for more details
Also see 07-CSHAddExpense, Iteration 1-3 for more details