Unnecessary concatenation with NULL value

Concatenating a VARCHAR2 value with NULL is no-op. So, the NULL value should be removed.

A concatenation of any other datatype with NULL will cause a implicit cast to VARCHAR2. If this is the desired behavior, replace the concatenation by a TO_CHAR call to make the intention explicit. See this example:

var := NVL(''||id, 'Empty');

You should use this:

var := NVL(TO_CHAR(id), 'Empty');