Hashtable.get() throws NullPointerException while key is not null.

Exception in thread "main" java.lang.NullPointerException
at java.util.Hashtable.get(Hashtable.java:455)
at java.util.Properties.getProperty(Properties.java:951)
at sun.jvm.hotspot.runtime.VM.getSystemProperty(VM.java:851)
at sun.jvm.hotspot.jdi.VirtualMachineImpl.version(VirtualMachineImpl.java:801)