Description of problem:
We have a block of code that processes a hash with a date key in "01/Jul/2022" format.  When we try to loop through the sorted keys with a sort procedure, we get  an error indicating that the parameter passed to the convert_month routine is not a string.  See the code below for a complete description.

hits hash
"01/Jul/2022"   Title1    4
"03/Jul/2022"   Title2    7
. . .

foreach $date (sort sortdate keys %hits){
 . . .
}

sub sortdate(){
    #parse the date format  DD/MMM/YYYY - i.e. 07/Feb/2019
    # into sortable key YYYY##DD - i.e. 20190207

    { substr($a,7,4) <=> substr($b,7,4) ||
      Decode_Month(substr($a,3,3)) <=>  Decode_Month(substr($b,3,3)) ||
      substr($a,0,2) <=> substr($b,0,2)
    }
}

When we run this, we get the following error:
Date::Calc::Decode_Month(): argument is not a string at ./xxx.pl line ###.  Which points to the line with the Decode_Month(substr($a,3,3)) 

I can work around the error by forcing the result of the substr() call to be a string.  Decode_Month("".substr($a,3,3)), but the type should have been set correctly without that, since substr returns the 3 character month string: Jan, Feb, ...

I put in extra debug prints and all of the keys in the hits array are valid date strings with a valid 3 char month abbreviation.

This code was ported over from Solaris and it is working fine there.

Version-Release number of selected component (if applicable): Date::Calc (6.4)


How reproducible:
Every time

Steps to Reproduce:
1.  See above code
2.
3.

Actual results:
Error message: Date::Calc::Decode_Month(): argument is not a string at ./xxx.pl line ###.

Expected results:
process sorted list of hash elements

Additional info: