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Appending to a list variable X should append the succeeding value(s) to X
regardless of whether X is currently empty or not.
Before:
  acid: l={}
  acid: append l, 1
  {0x00000001}
  acid: l
  acid: 
With this patch:
  acid: l={}
  acid: append l, 1
  {0x00000001}
  acid: l
  {0x00000001}
  acid: 
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