public static ValueUpdate createAdd(FieldValue value) {
        return new AddValueUpdate(value);
    }
Creates a new value update specifying an addition of a value to an array or a key to a weighted set (with default weight 1).

@param value the value to add to the array, or key to add to the weighted set
@return a ValueUpdate specifying the addition
@throws IllegalArgumentException      if the runtime type of newValue does not match the type required
@throws UnsupportedOperationException if the field type is not array or weighted set
document/src/main/java/com/yahoo/document/update/ValueUpdate.java