Github user jhorcicka commented on the issue:
https://github.com/apache/metamodel/pull/123
According to
https://docs.oracle.com/cd/B28359_01/server.111/b28318/datatype.htm#i3253 I
tried CHAR, NCHAR, CLOB, NCLOB, VARCHAR2 and NVARCHAR2. In these cases when an
empty string was assigned to the column, null was stored instead.
From what I read I think currently there is a general rule '' = null. It
might change in the future when Oracle tries to standardize VARCHAR.
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