Google Maps force close while re-opening application

Question

I make android application using google maps. But when I re-opening my app, it was force close. And i figure out that my app not going to force close when I clear my phone's memory or re-opening again. Does anyone can help me? This is the error message

java.lang.NullPointerException: Attempt to invoke interface method 'com.google.android.gms.maps.model.VisibleRegion com.google.android.gms.maps.internal.IProjectionDelegate.getVisibleRegion()' on a null object reference
                                                                                  at com.google.android.gms.maps.Projection.getVisibleRegion(Unknown Source)
                                                                                  at com.google.maps.android.clustering.view.DefaultClusterRenderer$RenderTask.run(DefaultClusterRenderer.java:376)
                                                                                  at java.lang.Thread.run(Thread.java:818)