@Override
    public Index getIndex(String name) {
        if ( ! importedField.fieldName().equals(name)) {
            throw new IllegalArgumentException("Getting an index (" + name + ") with different name than the imported field ("
                                               + importedField.fieldName() + ") is not supported");
        }
        String targetIndexName = importedField.targetField().getName();
        return importedField.targetField().getIndex(targetIndexName);
    }
Wraps {@link ImportedField} as {@link ImmutableSDField}.
Methods that are not meaningful or relevant for imported fields will throw {@link UnsupportedOperationException}.

@author bjorncs
config-model/src/main/java/com/yahoo/schema/document/ImmutableImportedSDField.java