Creates a new javafx.beans.binding.IntegerBinding that holds the length of a javafx.beans.value.ObservableStringValue.

Note: In this comparison a String that is null is considered to have a length of 0.

Parameters:

op

the ObservableStringValue

Returns:  the new IntegerBinding

Exceptions:

NullPointerException

if the ObservableStringValue is null

Since:  JavaFX 8.0