Errors while trying to simulate using more number of camers for a fog device in a serveillance system IoT application

[sujannou]

While trying to simulate one fog device(one router) using 100 cameras in a Fog-Based Cloud Network in a surveillance system IoT application, I got the following results
"
Placement of operator object_detector on device Router-0 successful.
Placement of operator object_tracker on device Router-0 successful.
Router-0 is shifting object_detector north.
Proxy-Server is shifting object_detector north.
Cloud is shifting object_tracker north.
Cloud is shifting object_detector north.
Placement of operator object_tracker on device Cloud successful.
Placement of operator user_interface on device Cloud successful.
Placement of operator object_detector on device Router-0 successful.
Router-0 is shifting object_detector north.
Cloud is shifting object_tracker north.
Proxy-Server is shifting object_detector north.
java.lang.NullPointerException
at org.fog.placement.ModulePlacementEdgewards.shiftModuleNorth(ModulePlacementEdgewards.java:303)
at org.fog.placement.ModulePlacementEdgewards.placeModulesInPath(ModulePlacementEdgewards.java:207)
at org.fog.placement.ModulePlacementEdgewards.mapModules(ModulePlacementEdgewards.java:73)
at org.fog.placement.ModulePlacementEdgewards.(ModulePlacementEdgewards.java:54)
at org.fog.Simulation.FogSurveillanceSystem.main(FogSurveillanceSystem.java:114)
"
Can anybody help me with some of my following queries based on above simulation results?

1. What does the following means and signify?
   a. Router-0 is shifting object_detector north.
   b. Cloud is shifting object_tracker north.
   c. Cloud is shifting object_detector north.
2. What does the following error means and how to fix them?
   "
   java.lang.NullPointerException
   at org.fog.placement.ModulePlacementEdgewards.shiftModuleNorth(ModulePlacementEdgewards.java:303)
   at org.fog.placement.ModulePlacementEdgewards.placeModulesInPath(ModulePlacementEdgewards.java:207)
   at org.fog.placement.ModulePlacementEdgewards.mapModules(ModulePlacementEdgewards.java:73)
   at org.fog.placement.ModulePlacementEdgewards.(ModulePlacementEdgewards.java:54)
   at org.fog.Simulation.FogSurveillanceSystem.main(FogSurveillanceSystem.java:114)

For router =1, no of cameras =5, I got the following normal results
" Placement of operator object_detector on device Router-0 successful.
Placement of operator object_tracker on device Router-0 successful.
Router-0 is shifting object_detector north.
Creating motion_detector on device Camera-0-4
Creating user_interface on device Cloud
Creating object_tracker on device Proxy-Server
Creating object_detector on device Proxy-Server
Creating motion_detector on device Camera-0-0
Creating motion_detector on device Camera-0-1
Creating motion_detector on device Camera-0-2
Creating motion_detector on device Camera-0-3"