Dimension too large when using forest package - too many null nodes?

When I use the following code

documentclass{article}
usepackage[edges]{forest}

begin{document}
    
begin{forest}
  for tree={
    grow'=east,
    anchor=west,
    font=itshape,
    forked edge,
    fork sep = 2mm, 
    l sep=4mm,
    s sep=2mm,
  },
  s sep=2mm,
 delay={   where content={}{coordinate}{}, },
  [XXX-root,
   [ % 1
    [ % 2
     [XXX-children-A
      [XXX-children-B]
      [XXX-children-C]
     ] 
     [XXX-children-D]
    ]
    [ % 3
     [XXX-children-E]
     [XXX-children-F
      [XXX-children-G]
       [ % 4
        [XXX-children-H]
        [XXX-children-I]
       ]
     ]
    ]
   ]
   [ % 5
    [ % 6
     [XXX-children-J]
     [XXX-children-K]
    ]
    [ % 7
      [XXX-children-L]
      [XXX-children-M
        [XXX-children-N]
        [ % 8
         [XXX-children-O]
         [ % 9
          [XXX-children-P]
          [ % 10
          [ % 11
             [XXX-children-Q]
             [XXX-children-S]
         ]
         [ % 12
            [XXX-children-T]
            [XXX-children-U]
          ]
          ]
         ]
        ]
      ]
    ] 
   ]
  ]
end{forest}
end{document}

Everything works fine. However, if I change the text in the nodes in the following code

documentclass{article}
usepackage[edges]{forest}

begin{document}
begin{forest}
  for tree={
    grow'=east,
    anchor=west,
    font=itshape,
    forked edge,
    fork sep = 2mm, 
    l sep=4mm,
    s sep=2mm,
  },
  s sep=2mm,
 delay={   where content={}{coordinate}{}, },
  [Nymphalidae,
   [ % 1
    [ % 2
     [Limenitidinae
      [Neptini]
      [Limenitidini]
     ]
     [Heliconiinae]
    ]
    [ % 3
     [Apaturinae]
     [Nymphalinae
      [Nymphalini]
       [ % 4
        [Junoniini]
        [Melitaeini]
       ]
     ]
    ]
   ]
   [ % 5
    [ % 6
     [Libytheinae]
     [Danainae]
    ]
    [ % 7
      [Charaxinae]
      [Satyrinae
        [Elymniini]
        [ % 8
         [Coenonymphini]
         [ % 9
          [Ypthimini]
          [ % 10
          [ % 11
             [Melanargiini]
             [Satyrini]
         ]
         [ % 12
            [Maniolini]
            [Erebiini]
          ]
          ]
         ]
        ]
      ]
    ]
   ]
  ]
end{forest}

end{document}

I get the error message
! Dimension too large.
pgf@x

If I change null nodes 11 and 12 to nodes with one or more characters in them everything works fine. This is very confusing, as the only difference between the two pieces of code is the text in each node.

documentclass{article}
usepackage[edges]{forest}

begin{document}
begin{forest}
  for tree={
    grow'=east,
    anchor=west,
    font=itshape,
    forked edge,
    fork sep = 2mm, 
    l sep=4mm,
    s sep=2mm,
  },
  s sep=2mm,
 delay={   where content={}{outer sep=0pt,inner sep=0pt,
    append after command={(tikzlastnode.west) edge (tikzlastnode.east)}}{}, },
  [Nymphalidae,
   [ % 1
    [ % 2
     [Limenitidinae
      [Neptini]
      [Limenitidini]
     ]
     [Heliconiinae]
    ]
    [ % 3
     [Apaturinae]
     [Nymphalinae
      [Nymphalini]
       [ % 4
        [Junoniini]
        [Melitaeini]
       ]
     ]
    ]
   ]
   [ % 5
    [ % 6
     [Libytheinae]
     [Danainae]
    ]
    [ % 7
      [Charaxinae]
      [Satyrinae
        [Elymniini]
        [ % 8
         [Coenonymphini]
         [ % 9
          [Ypthimini]
          [ % 10
          [ % 11
             [Melanargiini]
             [Satyrini]
         ]
         [ % 12
            [Maniolini]
            [Erebiini]
          ]
          ]
         ]
        ]
      ]
    ]
   ]
  ]
end{forest}

end{document}