NullPointerException when trying to get the coref

[resplendentfrever]

I am having the following issue when I am trying to get the coref. Can you please help me out
java.lang.NullPointerException
at corenlp.JsonPipeline.getCorefInfo(JsonPipeline.java:213)
at corenlp.JsonPipeline.processTextDocument(JsonPipeline.java:321)
at corenlp.SocketServer.runCommand(SocketServer.java:125)
at corenlp.SocketServer.parseAndRunCommand(SocketServer.java:165)
at corenlp.SocketServer.namedpipeLoop(SocketServer.java:253)
at corenlp.SocketServer.main(SocketServer.java:108)
Traceback (most recent call last):
File "", line 1, in
TypeError: 'NoneType' object has no attribute 'getitem'