core/src/main/java/com/orientechnologies/orient/core/sql/OChainedIndexProxy.java
private Set<Comparable> prepareKeys(OIndex<?> index, Object keys) {
    final OIndexDefinition indexDefinition = index.getDefinition();
    if (keys instanceof Collection) {
      final Set<Comparable> newKeys = new TreeSet<Comparable>();
      for (Object o : ((Collection) keys)) {
        newKeys.add((Comparable) indexDefinition.createValue(o));
      }
      return newKeys;
    } else {
      return Collections.singleton((Comparable) indexDefinition.createValue(keys));
    }
  }
private Set<Comparable> prepareKeys(OIndex<?> index, Object keys) {
    final OIndexDefinition indexDefinition = index.getDefinition();
    if (keys instanceof Collection) {
      final Set<Comparable> newKeys = new TreeSet<Comparable>();
      for (Object o : ((Collection) keys)) {
        newKeys.add((Comparable) indexDefinition.createValue(o));
      }
      return newKeys;
    } else {
      return Collections.singleton((Comparable) indexDefinition.createValue(keys));
    }
  }
Make type conversion of keys for specific index.

@param index - index for which keys prepared for.
@param keys  - which should be prepared.

@return keys converted to necessary type.