@Override
    public FieldValue applyTo(FieldValue fval) {
        if (fval instanceof CollectionFieldValue) {
            CollectionFieldValue val = (CollectionFieldValue) fval;
            val.removeValue(value);
        }
        return fval;
    }
Sets the key this should remove
document/src/main/java/com/yahoo/document/update/RemoveValueUpdate.java