I was recently teaching an Advanced SharePoint class in Richardson, TX and a student was expressing his frustration over Microsoft's apparent oversight within the SharePoint Designer workflow wizard. One of the "IF" conditions is a simple testing of the value of a field…"If this equals that." He wanted to test a date field in SharePoint to see if it was empty or not. Problem is, when you select a field that is typed as DATE in SharePoint Designer, there is no test for the empty or null condition. You can see this in the first figure.
It occurred to me that we might be able to change the type of the field to a string and then be able to perform the comparison. I used the "Build Dynamic String" action.
I selected the End Date custom field on my Expense Statements list and stored it in a new variable that was typed as STRING.
The results of this were not exactly what I expected, however I was able to determine, through trial and error (sending the values in an email), that the conversion created a string that was filled with question marks (????). Therefore, if you simply test to see if the new string begins with a ?, you can successfully test for an empty date value.
Both my student and I were happy with the results. There may be other ways to do this (perhaps by testing if the value of the date is equal to the "beginning of time" date), but this certainly seems like an easy and foolproof method.