@Override
    public boolean existsIndex(String name) {
        return importedField.targetField().existsIndex(name);
    }
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