Cause
You tried to index a row where at least one of the meta columns was NULL.
You tried to index a row where at least one of the meta columns was NULL.
provide a value for the meta column and reindex the row
Try the following links for this error:
http://docs.oracle.com/cd/E16655_01/server.121/e26079/drgus.htm
https://community.oracle.com/message/435642
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