fast formula to validate project fields are not null in Timecard

Summary:

Content (please ensure you mask any confidential information):

Need a fast formula to validate the project, task and expenditure type fields are not null upon timecard save and submit. These are all independent fields in layout.

These project fields cannot be made mandatory.

Thanks

Version (include the version you are using, if applicable):

24B

Code Snippet (add any code snippets that support your topic, if applicable):