Lua error in Module:category_tree/topic/Nature at line 335: bad argument #2 to 'format' (no value).

Backtrace:

[C]: in function "format"
Module:category_tree/topic/Nature:335: in function "init"
package.lua:103: in function "require"
Module:category_tree/topic/data:74: in function "init"
package.lua:103: in function "require"
Module:category_tree/topic:686: ?
(tail call): ?
Module:category_tree/poscatboiler:130: in function "initCommon"
Module:category_tree/poscatboiler:75: ?
(tail call): ?
Module:category_tree/poscatboiler:829: in function "canonicalize_parents_children"
Module:category_tree/poscatboiler:872: in function "getParents"
Module:category_tree:187: in function "show_breadcrumbs"
Module:category_tree:488: in function "generate_output"
Module:category_tree:605: in function "chunk"
mw.lua:527: ?
[C]: ?

Category:Siwa terms interfixed with -ust-

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