See test_emptyStringEntityTermInExpression_01

(which I recently modified to be a negative test, looking for a message about the incorrect use of %ES; in the terminator.)

If you have an expression for a terminator, and the expression returns a string containing %ES; by itself, that's not allowed (you can't "turn off" delimiters at runtime by specifying a delimiter to be empty string)

This should be a runtime SDE.