Reproducing code:

        OUTER:
        while (true) {
            for (OSProcess proc : ProcessTree.get()) {
                if (proc.hasMatchingEnvVars(Collections.singletonMap("foo", "bar"))) { //-------- fails with NPE
                    break OUTER;
                }
            }
        }

Analysis:
1. OSProcess#hasMatchingEnvVars assumes that OSProcess#getEnvironmentVariables never returns null (and its Javadoc says so).
2. There's a time frame between ProcessTree.get() and call to getEnvironmentVariables
3. If proccess exits during this timeframe, an exception is thrown by org.jvnet.winp.WinProcess#getEnvironmentVariables, propagated through WindowsOSProcess#getEnvironmentVariables2, then caught in WindowsOSProcess#getEnvironmentVariables
4. And finally, WindowsOSProcess#getEnvironmentVariables returns null, thus violating contract from superclass Javadoc.