The expression in VAL_ProgramItem_Dependencies can’t be evaluated (processed) because one side of the expression is null. You should check for isEmpty first and then evaluate the expression.
(the expression is indicated in the error)
This doesn't tell us much about the error..If you open the console view in the modeler (you can find that in "View>Console"), you can see what is going wrong.
You need to look in the server log (in this case your modeller console log) to see what the actual error was (with stacktrace) if you can post that here we can help you.
THank you for your help