Message Oracle ORA-36691 - (NTEXTCNV02) Invalid escape sequence in argument to UNISTR function: string.

ERROR(NTEXTCNV02) Invalid escape sequence in argument to UNISTR function: string.
CAUSEThe user called the UNISTR function on a string that had an invalid escape sequence. The only valid escape sequences in UNISTR are 1.) an escape-escape sequence, and 2.) an escape, followed by exactly four hexadecimal digits.
ACTIONMake sure that all escape sequences in UNISTR arguments are exactly four hexadecimal digits. To represent codepoints whose value is less than 0x1000, use preceding zeros. WRONG: 0x10; RIGHT: 0x0010.