Round trip of SBOLTestSuite/SBOL2_nc/SBOL1and2Test.xml fails

[tcmitchell]

The round trip test for SBOLTestSuite/SBOL2_nc/SBOL1and2Test.xml fails with a ValueError in lxml.etree when serializing the document:

ValueError: Invalid namespace prefix ''

[bbartley]

This test file has always failed and probably could be marked as an expected failure.

It is an extreme edge case in which SBOL v1 and SBOL v2 data is mixed into a single XML file. Although this is theoretically valid, in practice, there has been no user demand for such a feature, and it would be a major detour to try and implement it