@Override
    protected void checkCompatibility(DataType fieldType) {
        if (!(fieldType instanceof CollectionDataType)) {
            throw new UnsupportedOperationException("Expected collection, got " + fieldType.getName() + ".");
        }
        fieldType = ((CollectionDataType)fieldType).getNestedType();
        if (value != null && !value.getDataType().equals(fieldType)) {
            throw new IllegalArgumentException("Expected " + fieldType.getName() + ", got " +
                                               value.getDataType().getName());
        }
    }
Return the associated weight of this value update.

@return the weight of this value update, or 1 if unset
document/src/main/java/com/yahoo/document/update/AddValueUpdate.java