It's probably a bug (and certainly not desirable). I've reported it. The only workaround I can find at the moment is to use "\xa0" (a single non-breaking space) where no data is available. Like so:

#! /usr/bin/perl -w
use strict;
use 5.010;

use Perl6::Form;

my @last = qw(Smith Jones Wright Wong Evans McFee Ho Nuygen Willians H
+owlett Jones Peters Milford Tam Lam Soma Egon Wilson);
my @first = qw(Jim Jack Wendy Lee Bo Lenord Jan Dana Lindy Kyle Nora J
+ane Bill Woo John Mick Lazlo Jenna);
my @mid   = ("\xa0", "\xa0", 'A', "\xa0", "B", "\xa0", "\xa0", 'A', "\
+xa0", "B", "\xa0", "\xa0", 'A', "\xa0", "B", "\xa0", "\xa0", 'A');
my @suf   = ("") x 18;
my @nick = qw(Jim Jack Wendy Lee Bo Lenord Jan Dana Lindy Kyle Nora Ja
+ne Bill Woo John Mick Lazlo Jenna);
my @ID = 1..18;

print form
    { 
      page => { length => 15,
                number => 1,
                feed => "\f",
                footer =>            "________________________________
+_____________________________________\n",
                header => { first => "================================
+=====================================\n"
                                   . "|                   xxxxxxxxxxxx
+xxxxxxxxxxxxxxxx                    |\n"
                                   . "|                     xxxxxxxxxx
+xxxxxxxxxxxx                        |\n"
                                   . "|                               
+                                    |\n"
                                   . "|                          List 
+of Players                          |\n"
                                   . "|===============================
+====================================|\n"
                                   . "|Last                |First     
+          |MI|Suffix|Nickname  |  ID|\n"
                                   . "|_______________________________
+____________________________________|",
                          other =>   "================================
+=====================================\n"
                                   . "|                          List 
+of Players                          |\n"
                                   . "|===============================
+====================================|\n"
                                   . "|Last                |First     
+          |MI|Suffix|Nickname  |  ID|\n"
                                   . "|-------------------------------
+------------------------------------|",
                     }
            }
    },
    "| {]]]]]]]]]]]]]]]]} | {]]]]]]]]]]]]]]]]} |{}| {II} | {]]]]]]} | 
+{} |\n",
        \@last,              \@first,          \@mid,\@suf, \@nick,  \
+@ID;
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