From @zoffixznet

The issue I encountered is a case where when I assign a default created using infix​:<xx> op,
inside the `where` clause, it's not yet failed over, so I got exhausted Seq errors​:

  <Zoffix__> m​: -> +@​commands, :@​in where {dd $_; 1} = Nil xx 1 { @​in.elems }([])
  <camelia> rakudo-moar 61ecfd​: OUTPUT​: «(Nil,).Seq␤»

Looking at it further, however, it appears most of the time it Does The Right Thing;
and in fact, seems to be affected by unrelated things, such as whether there's
another parameter before it and whether it got a `+` slurpy on it​:

  <Zoffix__> m​: -> @​commands, :@​in where {dd $_; 1} = Nil xx 1 { @​in.elems }([])
  <camelia> rakudo-moar 61ecfd​: OUTPUT​: «(Nil,)␤»
  <Zoffix__> m​: -> :@​in where {dd $_; 1} = Nil xx 1 { @​in.elems }()
  <camelia> rakudo-moar 61ecfd​: OUTPUT​: «(Nil,)␤»