Yup, just submitted a pull request.
In the commit I included some additional notes about the feature requirements checking for this method (primarily, that the check for ADD_PROPERTY support on vertices is implicit, because the SIMPLE feature set doesn't check for that directly, but rather for being able to add meta properties).
Also, I just saw in the SIMPLE feature set that a check is made for Graph.Features.VertexPropertyFeatures.FEATURE_STRING_VALUES. Is this if statement check in the unit test code itself even needed then in the first place? If not, perhaps the right thing to do is to delete it all together (in which case you'll want to disregard my PR which simply fixes the if statement check).