Oracle - Handle empty resultset on IF THEN ELSE statement

which should be the IF condition when the variable assignation results from an empt开发者_开发知识库y resultset?

Example:

CREATE OR REPLACE Function get_values
     ( chv_input IN varchar2 )
     RETURN varchar2
IS
     chv_output varchar2(100);

  BEGIN

select 'value'
    into chv_output
from dual where 1=2; 

IF chv_output is null THEN --this condition is not working

    chv_output := 'null';

ELSE
     chv_output := 'not null';

END IF;

  RETURN chv_output;

END;

--select 1, get_values('112') from dual

Try this instead:

EXCEPTION
WHEN NO_DATA_FOUND
  chv_output := 'null';