Drools throws NullPointerException in retractLeftTuple()

Issue

• Drools application throws NullpointerException

• The root exception is :

  Caused by:
  null
      at org.drools.reteoo.RightInputAdapterNode.retractLeftTuple(RightInputAdapterNode.java:154)
      at org.drools.reteoo.SingleLeftTupleSinkAdapter.doPropagateRetractLeftTuple(SingleLeftTupleSinkAdapter.java:217)
      at org.drools.reteoo.SingleLeftTupleSinkAdapter.propagateRetractRightTuple(SingleLeftTupleSinkAdapter.java:124)
      at org.drools.reteoo.JoinNode.retractRightTuple(JoinNode.java:151)
      at org.drools.reteoo.ModifyPreviousTuples.retractTuples(ModifyPreviousTuples.java:132)
      at org.drools.reteoo.EntryPointNode.modifyObject(EntryPointNode.java:176)
      at org.drools.common.AbstractWorkingMemory.update(AbstractWorkingMemory.java:1442)
      at org.drools.common.AbstractWorkingMemory.update(AbstractWorkingMemory.java:1349)
      at org.drools.base.DefaultKnowledgeHelper.update(DefaultKnowledgeHelper.java:183)
      at org.drools.base.DefaultKnowledgeHelper.update(DefaultKnowledgeHelper.java:196)