public static FieldUpdate createDecrement(Field field, Number decrement) {
        return new FieldUpdate(field, ValueUpdate.createDecrement(decrement));
    }
Creates a new field update, with one encapsulated value update that decrements a value.
Note that the data type must be a numeric type.

@param field     the field to decrement the value of
@param decrement the number to decrement by
@return a FieldUpdate specifying the decrement
@throws UnsupportedOperationException if the data type is non-numeric
@see ValueUpdate#createDecrement(Number)
document/src/main/java/com/yahoo/document/update/FieldUpdate.java