Creates a new javafx.beans.binding.ObjectBinding that contains the mapping of a specific key in an javafx.collections.ObservableMap.

Parameters:

op		the ObservableMap
key		the key in the Map
<K>		type of the key elements of the Map
<V>		type of the value elements of the Map

Returns:  the new ObjectBinding

Exceptions:

NullPointerException

if the ObservableMap or key is null

Since:  JavaFX 2.1