Oracle® Database 11g / 12c / 18c error codes EXP-00042: Missing NLS_CHARACTERSET/NLS_NCHAR_CHARACTERSET in props$

EXP-00042: Missing NLS_CHARACTERSET/NLS_NCHAR_CHARACTERSET in props$

Oracle Error Code: EXP-00042

Cause: A value for NLS_CHARACTERSET/NLS_NCHAR_CHARACTERSET was not entered in the props$ table"

Action: internal error.