How to set default value of date input parameter in procedure if they are null?

I am having a Procedure , which is accepting fromDate and toDate input parameters I need to set default values as First date of Last month and last date of previous month respectively. I am trying to use below code, but still proper default dates are not being set. Please let me know if below code is valid or i can do something to correct it:

 create or replace PROCEDURE        "TEST" 
        (
         fromdate_in              IN varchar2,
         todate_in                IN varchar2,
         type_in              IN number DEFAULT 01
        )
    is

        V_date              varchar2(3000);

    begin

        select to_date(fromdate_in) into V_date from dual; -- Correct date entered

        Exception WHEN Others THEN
        select to_char(trunc(trunc(sysdate, 'MM') - 1, 'MM'),'DD/MM/RRRR') into V_date from dual; -- if fromdate_in --is null then set V_date to first date of Previous month

        -- calculations using V_date

    end TEST;

Please note , I have shown only how I am setting first date of Previous month to From Date for simplicity.

You could do it much easier like this:

create or replace PROCEDURE        "TEST" 
    (
     fromdate_in              IN DATE,
     todate_in                IN DATE,
     type_in              IN number DEFAULT 1
    )
is

    V_date              DATE;

begin

    V_date := NVL(fromdate_in, TRUNC(ADD_MONTHS(SYSDATE, -1), 'MM'));
    -- calculations using V_date

end TEST;

If you are forced to use VARCHAR2 for fromdate_in then convert the value to DATE:

V_date := NVL(TO_DATE(fromdate_in, 'DD/MM/YYYY'), TRUNC(ADD_MONTHS(SYSDATE, -1), 'MM'));