public NumberExpression<Double> z() {
        if (z == null) {
            z = Expressions.numberOperation(Double.class, SpatialOps.Z, mixin);
        }
        return z;
    }
public NumberExpression < Double > z ( ) { if ( z == null ) { z = Expressions . numberOperation ( Double . class , SpatialOps . Z , mixin ) ; } return z ; }
The z-coordinate value for this Point, if it has one. Returns NIL otherwise.

@return z-coordinate