handle null values in shapefile input field by converting them to zero
Revert "handle null values in shapefile input field by converting them to zero"

This reverts commit 214f948d50d7c5f084b317bda607bb7323844524.
handle null valued in shapefile input field by defaulting to zero
Avoid race condition and null pointer error caused by temporary edges created with one RoutingContext being visible to other RoutingContexts
initial work on MultipleThresholdCumulativeAggregator