Minor Description
The IndexTool has several modes. If the -direct or -partial-rebuild flags are not set, the tool assumes the user wants to rebuild the index by creating HFiles and then bulk-loading them back into HBase, and requires an extra -output-path flag to deterine where the temporary HFiles should live.
In practice, we've found that -direct mode (which loads using HBase Puts) is quicker. However, even though there's logic to not require the -output-path flag when -direct mode is chosen, the IndexTool will throw an NPE if it's not present.