Expressions passed to this function must have one of the following data types:
- source_string = VARCHAR or CLOB
- length = INTEGER, BIGINT, or NUMBER
- fill_string = CHAR, VARCHAR, or CLOB
If any of the input arguments are NULL, the function returns NULL.
You can also pass arguments with data types that can be converted to the above types using the implicit data type conversion rules that apply to UDFs.