Input to "valid to" and "valid from" dates is mandatory for frequency type "every" only

Current Situation

• When users insert the "Valid From" and "Valid To" dates inside the "Add Frequency" popup for any frequency type different from "every" and unselect dates then the GUI throws an error message in red color: "Input to this field is required." See attached add_frequency_popup.png.

Desired behavior

• Except for the frequency type "every" it should not be mandatory to specify the "Valid From" and "Valid To" dates.