Returns a javafx.beans.binding.StringExpression that wraps a javafx.beans.value.ObservableValue. If the ObservableValue is already a StringExpression, it will be returned. Otherwise a new javafx.beans.binding.StringBinding is created that holds the value of the ObservableValue converted to a String.

Parameters:

observableValue

The source ObservableValue

Returns:  A StringExpression that wraps the ObservableValue if necessary

Exceptions:

NullPointerException

if observableValue is null