public static ValueUpdate createDecrement(FieldValue key, Number decrement) {
        return createMap(key, createDecrement(decrement));
    }
Creates a new value update that decrements a weight in a weighted set. Note that this method is just a convenience
method, it simply creates a decrement value update by calling createDecrement() and then creates a map value
update by calling createMap() with the key and the decrement value update as parameters.

@param key the key whose weight in the weighted set to decrement
@param decrement the number to decrement by
@return a ValueUpdate specifying the decrement
@see ValueUpdate#createDecrement(Number)
@see ValueUpdate#createMap(FieldValue, ValueUpdate)
document/src/main/java/com/yahoo/document/update/ValueUpdate.java