private boolean hasMultiValueField(FieldSet fieldSet) {
        for (ImmutableSDField field : fieldSet.fields()) {
            if (field.getDataType().isMultivalue())
                return true;
        }
        return false;
    }
Returns whether a particular command is prsent in this index info
config-model/src/main/java/com/yahoo/schema/derived/IndexInfo.java