sbol-10204 does not capture null displayId values

[jakebeal]

If you ask compliant URI to validate a null displayId, it will complain that your displayId has the wrong format, rather than complaining that it's missing:

libSBOLj/core2/src/main/java/org/sbolstandard/core2/URIcompliance.java

Line 44 in e8ac28e

throw new SBOLValidationException("sbol-10204");

[cjmyers]

Is this one also related to the URIs that end with slash?

[jakebeal]

This was discovered while trying to sort out this problem, but is a separate issue.