Use of uninitialized value in subroutine entry..

You should see at least a line number associated with this warning (not error) message, and it should be fairly easy to zero in on the argument the subroutine is expecting and not getting.

my $typehint_raws = [ ($typehint_raw) x  @$hashref];

If @$hashref is indeed a hash reference, I don't see how the code runs beyond that statement.

Win8 Strawberry 5.8.9.5 (32)  Wed 05/11/2022 21:07:27
C:\@Work\Perl\monks
>perl

use strict;
use warnings;

my $hr = { qw(a b  c d) };

print "got here \n";
print @$hr, "\n";
# print %$hr, "\n";  # works
print "and here \n";

^Z
got here
Not an ARRAY reference at - line 8.
[download]

To be clear,I left the line number out because it means nothing, but it is definitely on the line:

my $json = encode_json($arrayref, $typehint_raws);

Using print Dumper I verify that:
*$typehint_raws becomes one empty array for each record found
*$typehint_raw is a hash which has each column and and whether it's an int or string

Once again, everything works, but each call to the above line returns that error.

Here's the code I use to retrieve each record....

$data = readRaw(table name);

sub readRaw {
    my ($rawfilename) = @_;

    my $dbCommand = 'select '.join ',', @rawFields;
    $dbCommand .= qq^ from $rawfilename;^;

    $dbHandle=$db->prepare($dbCommand);
    $dbHandle->execute();

    my $data = $dbHandle->fetchall_arrayref();
    $dbHandle->finish;

    foreach my $rows (@$data) {
            my %GenericData;
            @GenericData{ @rawFields } = @$rows; # NOTE added

            push @rawRecords, \%GenericData;
        }

     return \@rawRecords;
}
[download]

So I have an array of arrays, but each array holds the reference to a hash for each record read

And $data is passed to this function

sub makeJSONToExport {
    my ($arrayref) = @_;

    my $typehint_raw =  { age        => JSON_TYPE_INT,
            lastname      => JSON_TYPE_STRING,
            firstname          => JSON_TYPE_STRING};


    my $typehint_raws = [ ($typehint_raw) x  @$arrayref];
    my $json = encode_json($arrayref, $typehint_raws);
    return $json;
}
[download]

Once again, everything works, but each call to the above line returns that error.

As AnomalousMonk has already pointed out, this isn't an error - it's a warning. There is a singificant difference between the two which is important to understand.

The solution is to filter or modify your data such that you do not send uninitialized values into the subroutine.

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🦛