Resolve "Measurements if no Agent is in the measurement area"

VadereSimulator/src/org/vadere/simulator/projects/dataprocessing/processor/AreaSpeedProcessor.java

@@ -50,7 +50,8 @@ public class AreaSpeedProcessor extends AreaDataProcessor<Double> {
             }
         }
 
-        this.putValue(new TimestepKey(step), (pedCount > 0 ? sumVelocities / pedCount : 0.0));
+        // Insert a NaN value if there are no agents available (see #287)
+        this.putValue(new TimestepKey(step), (pedCount > 0 ? sumVelocities / pedCount : Double.NaN));
     }
 
     @Override

VadereSimulator/tests/org/vadere/simulator/projects/dataprocessing/processor/AreaSpeedProcessorTestEnv.java

@@ -115,7 +115,9 @@ public class AreaSpeedProcessorTestEnv extends ProcessorTestEnv<TimestepKey, Dou
 				when(state.getSimTimeInSec()).thenReturn(simTime);
 
 				int step = state.getStep();
-				addToExpectedOutput(new TimestepKey(step), 0.0);
+
+				// if no agent is in the area, then return NaN (see #287)
+				addToExpectedOutput(new TimestepKey(step), Double.NaN);
 			}
 		});
 	}