Syntax options:

    RETURNS NULL ON NULL INPUT | CALLED ON NULL INPUT

    These clauses control how an external function is invoked when
    one or more of the function arguments is NULL. The CALLED ON
    NULL INPUT clause specifies that the function should be executed
    normally. A normal execution when the PARAMETER STYLE GENERAL
    clause is specified means that SQL should return a run-time error
    when the NULL value is detected.

    The RETURNS NULL ON NULL INPUT clause instructs Oracle Rdb to
    avoid the function call and just return a NULL result. This
    option is valuable for library functions such as SIN, COS,
    CHECKSUM, SOUNDEX, and so on, that usually return an UNKNOWN
    result if an argument is NULL.

    The CALLED ON NULL INPUT clause is the default.