IF formulas for date fields

[#1]

I want to write an expression for a chart that says if the bill date field is populated, sum the total request amount. I have most of it but I don't know what to put in place of 'Billed'. Any suggestions?

=sum(if([[Bill Date]]= 'Billed', [Total Request Amount]))

[nagaiank]

Try

=sum(if(Len(trim([Bill Date]))>0, [Total Request Amount]))

[#3]

Hmmm...I underestimated the complexity.

I want to show a few things:

Invoices with LOG

Sum (Total Request Amount) if LOG Received (checkbox) = Yes and Invoice Received (checkbox) = Yes and Bill Date (date) = Blank.

Missing a LOG

Sum (Total Request Amount) if LOG Received (checkbox) = No and Invoice Received (checkbox) = Yes and Bill Date (date) = Blank.

Missing an Invoice

Sum (Total Request Amount) if LOG Received (checkbox) = Yes and Invoice Received (checkbox) = No and Bill Date (date) = Blank.