public static ValueUpdate createDecrement(Number decrement) {
        return new ArithmeticValueUpdate(ArithmeticValueUpdate.Operator.SUB, decrement);
    }
Creates a new value update that decrements a value. Note that the data type must be a numeric
type.

@param decrement the number to decrement by
@return a ValueUpdate specifying the decrement
@throws UnsupportedOperationException if the data type is non-numeric
document/src/main/java/com/yahoo/document/update/ValueUpdate.java