I am seeing an error with substring functions in XPath. This may be fixed with DPath but the functions are not fully implemented yet.

This error is occuring when an element uses a substring function in the inputValueCalc that references other elements and the function returns an empty string. Instead of having an empty element in the resulting infoset the following error is thrown:

[error] Test edu.illinois.ncsa.daffodil.section23.dfdl_expressions.TestDFDLExpressionsDebug.test_substring_07 failed: edu.illinois.ncsa.daffodil.processors.ParseError: Parse Error: Expression evaluation failed. Details: javax.xml.xpath.XPathExpressionException: Expression result is not a node

See tests:
test_substring_07
test_substringbefore_04
test_substringbefore_05
test_substringafter_04
test_substringafter_05

In files:
daffodil-test/src/test/resources/edu/illinois/ncsa/daffodil/section23/dfdl_functions/Functions.tdml
daffodil-test/src/test/scala-debug/edu/illinois/ncsa/daffodil/section23/dfdl_expressions/TestDFDLExpressionsDebug.scala