Java "java.lang.NullPointerException" hatası

java.lang.IllegalMonitorStateException

        at java.lang.Object.wait(Native Method)

        at java.lang.Object.wait(Unknown Source)

        at groax.Launcher.main(:46126)

        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)

        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)

        at java.lang.reflect.Method.invoke(Unknown Source)

        at java.lang.invoke.MethodHandleImpl$BindCaller$T/1867750575.invoke_V(Unknown Source)

        at Network.main()

Exception in thread "main" java.lang.reflect.InvocationTargetException

        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)

        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)

        at java.lang.reflect.Method.invoke(Unknown Source)

        at java.lang.invoke.MethodHandleImpl$BindCaller$T/1867750575.invoke_V(Unknown Source)

        at Network.main()

Caused by: java.lang.NullPointerException

        at groax.Launcher.main(:49618)

        ... 6 more