A dependency string such as "virtual/jdk:*" (see e.g. bug 785436) causes an error message from depend-java-query:
$ depend-java-query --get-vm 'virtual/jdk:*'
!!! ERROR: could not convert string to float: '*'
I don't know whether it's okay to have a wildcard for this purpose, but if not, it should at least give a better error message than that.
the problem is not the wildcard itself but the fact that there is no version specified. this is not valid and not supported. it should be something like <=virtual/jdk-1.8:*". it sure might detect this kind of invalid version specification and report that appropriately.