java.lang.NullPointerException
    at Maze.getNumRandOccupants(Maze.java:118)
    at P4TestDriver.testMaze(P4TestDriver.java:995)
    at P4TestDriver.main(P4TestDriver.java:116)
    at __SHELL8.run(__SHELL8.java:7)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at bluej.runtime.ExecServer$3.run(ExecServer.java:814)
java.lang.NullPointerException
    at Maze.addRandomOccupant(Maze.java:130)
    at P4TestDriver.testMazeReadWrite(P4TestDriver.java:1071)
    at P4TestDriver.main(P4TestDriver.java:127)
    at __SHELL8.run(__SHELL8.java:7)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at bluej.runtime.ExecServer$3.run(ExecServer.java:814)