public static FieldUpdate createDecrement(Field field, FieldValue key, Number decrement) {
        return new FieldUpdate(field, ValueUpdate.createDecrement(key, decrement));
    }
Creates a new field update, with one encapsulated value update that decrements a weight in a weighted set.

@param field     the field to decrement one of the weights of
@param key the key whose weight in the weighted set to decrement
@param decrement the number to decrement by
@return a FieldUpdate specifying the decrement
@throws IllegalArgumentException if key is not equal to the nested type of the weighted set
@see ValueUpdate#createDecrement(Number)
@see ValueUpdate#createMap(FieldValue, ValueUpdate)
document/src/main/java/com/yahoo/document/update/FieldUpdate.java