Trying to get my head around moose and running into a problem. Cut down version of code

package AXRecord;

# Our libraries
use lib 'C:\Users\Jay\Desktop\SBS DEV\CODE\perl\Utilities';
use AXControl;
use AXSQL;
use Moose;
use DBI;

# Attributes
has 'Keys' => (is => 'rw', isa=>'ArrayRef');

# Contains a single record

sub BUILD
# Constructor
{
}
sub Select
    {
    
    #Get the primary key fields        
    $self->Keys (());
    $sql = AXSQL->new(ControlObject => $self->ControlObject, SQLString
+ => "SELECT column_name FROM information_schema.`key_column_usage` WH
+ERE table_name = '" . $self->Name . "' order by ordinal_position");
    $i = 1;
    while (($Col) = $sql->Fetch())
        {
        $self->Keys()->[$i] = $Col;
        $i++;
        }
    
    $Cnt = scalar $self->Fields;
    $self->FieldCount = $Cnt;
    $self->Changed = -1;
    }
1;
[download]

Problem is in the select method where I try to build the keys array. Specifically where I'm adding elements with the statements

$self->Keys()->[$i] = $Col;
[download]

The error message I'm getting is

Can't use an undefined value as an ARRAY reference at C:\Users\Jay\Des
+ktop\SBS DEV\CODE\perl\Utilities/AXRecord.pm line 106.

C:\Users\Jay\Desktop\SBS DEV\CODE\perl>
[download]

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