CLOB is null but it fails null check

Question

I have a clob variable which I'm checking for nullity. But it doesn't pass the null check.

  temp_appid_holder := NULL;

  if(temp_appid_holder = NULL) then
      dbms_output.put_line('temp is null');
  else 
      dbms_output.put_line('temp is not null');
  end if

The above control structure only prints 'temp is not null'.

I've tried printing the value of 'temp_appid_holder' but it prints nothing which means it's null.