Setting spacing alist key individually breaks annotate-spacing

[Mark Polesky]

\version "2.13.36"

\paper {
  annotate-spacing = ##t

  % this style works only if annotate-spacing is off:
  top-system-spacing #'minimum-distance = #20

  % this style works whether annotate-spacing is on
  % or off, but is not a valid workaround since it
  % unsets any alist keys that were previously set:
  %   top-system-spacing = #'((space . 5))
}

{ c'' }


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Here's the error message:

Drawing systems...
[...]/scm/stencil.scm:667:41:
In procedure assoc in expression (assoc-get sym spacing-spec ...):
[...]/scm/stencil.scm:667:41:
Wrong type argument in position 2 (expecting association list):
 ((minimum-distance . 20) . #<variable 7f0fed213210 value: #0#>)

shell returned 1

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Thanks.
- Mark