NOTE: this issue is with the "serializatoin-with-dpath2" branch, not the current 0.15.0 branch.

I wrote test not_04 to test the following: "If $arg is...a node with [nilled] true, fn:not returns true"
I set up a sequence where the first element is a nillable string (nameVal), and the second is a boolean with inputValueCalc set to fn:not(nameVal). This test only works against the current implementation with XPath when I cast nameVal to a string, but when I run it against the dpath2 branch, I get the following error:

[error] Test edu.illinois.ncsa.daffodil.section23.dfdl_expressions.TestDFDLExpressions.test_not_04 failed: edu.illinois.ncsa.daffodil.dsom.SchemaDefinitionError: Schema Definition Error: Value has not been set.

Please see test not_04 in the following file:
daffodil-test/src/test/resources/edu/illinois/ncsa/daffodil/section23/dfdl_functions/Functions.tdml