Thanks for the response tobyink.
I'm starting to see now that maybe the addition of MooseX::UndefTolerant might have helped- not sure yet. I am getting this error from my test file, but the line it is complaining about is in the following subroutine:

my $class = shift;
      my (%args) = validated_hash(
          \@_,
          id          => { isa => 'Int' },
          ticket_user => { isa => 'Customer::TicketUser' },
      );
  
      my $ticket_response = $class->_ticket_api_request(
          {
              method => 'get',
              route  => 'user/'
                . $args{ticket_user}->user_id
                . '/ticket/'
                . $args{id},
              data => undef,
          }
      );
  
      my $ticket = $class->new(
          {
              id              => $args{id},
              department_name => $ticket_response->{ticket}{department
+},
              subject         => $ticket_response->{ticket}{subject},
              status_id       => $ticket_response->{ticket}{status},
              created_time    => $ticket_response->{ticket}{created_ti
+me},
              ticket_user     => $args{ticket_user},
          }
      );
  
      my $posts_response = $class->_ticket_api_request(
          {
              method => 'get',
              route  => 'user/'
                . $args{ticket_user}->user_id
                . '/ticket/'
                . $args{id}
                . '/posts',
              data => undef,
          }
      );
  
      my @posts;
      for my $post_id ( keys $posts_response ) { # HERE
          my $post = GBClient::Model::Support::Ticket::Post->from_json
+(
              {
                  ticket => $ticket,
                  json   => $posts_response->{$post_id}
              }
          );
          push @posts, $post;
      }
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