@Override
  protected RegionConfig.Index fromNonNullConfigObject(Index index) {
    RegionConfig.Index regionConfigIndex = new RegionConfig.Index();
    regionConfigIndex.setName(index.getName());
    regionConfigIndex.setFromClause(index.getRegionPath());
    regionConfigIndex.setExpression(index.getExpression());

    if (index.getIndexType() == IndexType.KEY) {
      regionConfigIndex.setKeyIndex(true);
    } else if (index.getIndexType() == IndexType.HASH_DEPRECATED) {
      regionConfigIndex.setType(HASH);
    } else {
      regionConfigIndex.setType(RANGE);
    }

    return regionConfigIndex;
  }
based on the cache.xsd, index type can have only two values "range", "hash"
<attribute name="type" default="range">
<simpleType>
<restriction base="{http://www.w3.org/2001/XMLSchema}string">
<enumeration value="range"/>
<enumeration value="hash"/>
</restriction>
</simpleType>
</attribute>
geode-core/src/main/java/org/apache/geode/management/internal/configuration/converters/IndexConverter.java