Error: Underlying DBMS error - ORA-01400: cannot insert NULL into...
Importing a personal geodatabase layer to an Oracle ArcSDE geodatabase returns:
"Underlying DBMS error [ORA-01400: cannot insert NULL into
Failed to execute (Append)."
Oracle is unable to distinguish between null values and empty strings for 'Not Null' fields in specific data formats.
Solution or Workaround
Change the null values of the data source to an explicit space, such as a quoted single space. This can be done with a WHERE clause, as described in Esri Knowledge Base article 40255.