It's difficult to know what's causing the error without seeing a bit more information.

Are you sure you've created graph_pane correctly?

Try putting this near the beginning of your code:

use Data::Dumper;
$Data::Dumper::Indent = 1;
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and just before the line where the error occurs (Can't call method "gridSize" on an undefined value at tes7 line 23) put this:

printf "graph_pane => %s\n", Dumper(\$graph_pane);
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Assuming that graph_pane was assigned correctly, it should display the entire underlying data structure.  For example, I get:

graph_pane => $VAR1 = \bless( {
    'SubWidget' => {
      'scrolled' => bless( {
        '_After_' => {
          'after#3' => bless( [
            ${$VAR1}->{'SubWidget'}->{'scrolled'},
            'after#3',
            'idle',
            'once',
            bless( [
              'Manage',
              ${$VAR1}->{'SubWidget'}->{'scrolled'},
              bless( {
                # 
                # ...Many lines omitted...
                #
  }, 'Tk::Frame' );
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Did you get something like the above, or something completely different?

well, I got this:

graph_pane => $VAR1 = \bless( {
    '_Destroy_' => [
      bless( [
        sub { "DUMMY" }
      ], 'Tk::Callback' )
    ],
    'SubWidget' => {
      'frame' => bless( {
        'Configure' => {
          '-background' => '#C6C6B2B2A8A8',
          '-foreground' => '#000000000000',
          '-labelVariable' => undef
        },
        '_#canvas' => 11,
        '_TkValue_' => '.frame.frame',
        'ConfigSpecs' => {
          '-fg' => '-foreground',
          '-background' => [
            [
              'SELF'
            ],
            'background',
            'Background',
            '#C6C6B2B2A8A8'
          ],
          '-label' => [
            'METHOD',
            undef,
            undef,
            undef
          ],
          '-bg' => '-background',
          '-foreground' => [
            [
              'PASSIVE'
            ],
            'foreground',
            'Foreground',
            '#000000000000'
          ],
          'DEFAULT' => [
            'SELF'
          ],
          '-labelPack' => [
            'METHOD',
            undef,
            undef,
            undef
          ],
          '-labelVariable' => [
            'METHOD',
            undef,
            undef,
            undef
          ]
        }
      }, 'Tk::Frame' )
    },
    '_#frame' => 0,
    'Configure' => {
      '-background' => '#C6C6B2B2A8A8',
      '-foreground' => '#000000000000',
      '-scrollbars' => 'osoe',
      '-labelVariable' => undef
    },
    'Delegates' => {
      'DEFAULT' => ${$VAR1}->{'SubWidget'}->{'frame'},
      'bindtags' => ${$VAR1}->{'SubWidget'}->{'frame'},
      'bind' => ${$VAR1}->{'SubWidget'}->{'frame'}
    },
    '_After_' => {
      'after#1' => bless( [
        ${$VAR1},
        'after#1',
        'idle',
        'once',
        bless( [
          ${$VAR1},
          'packscrollbars'
        ], 'Tk::Callback' )
      ], 'Tk::After' )
    },
    '_TkValue_' => '.frame',
    '-scrollbars' => 'osoe',
    'ConfigSpecs' => {
      '-fg' => '-foreground',
      '-background' => [
        ${$VAR1}->{'SubWidget'}->{'frame'},
        'background',
        'Background'
      ],
      '-label' => [
        'METHOD',
        undef,
        undef,
        undef
      ],
      '-bg' => '-background',
      '-foreground' => [
        ${$VAR1}->{'SubWidget'}->{'frame'},
        'foreground',
        'Foreground'
      ],
      'DEFAULT' => [
        ${$VAR1}->{'SubWidget'}->{'frame'}
      ],
      '-labelPack' => [
        'METHOD',
        undef,
        undef,
        undef
      ],
      '-scrollbars' => [
        'METHOD',
        'scrollbars',
        'Scrollbars',
        'se'
      ],
      '-labelVariable' => [
        'METHOD',
        undef,
        undef,
        undef
      ]
    },
    'pack_pending' => 1
  }, 'Tk::Frame' );
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I completely doesn't know what it says...|||