@private Basically `Ripper.sexp` generates arrays whose first element is a symbol (type of sexp), but it exceptionally generates typeless arrays for expression sequence:

Ripper.sexp(‘foo; bar’)

> [

  :program,
  [ # Typeless array
    [:vcall, [:@ident, "foo", [1, 0]]],
    [:vcall, [:@ident, "bar", [1, 5]]]
  ]
]

We wrap typeless arrays in this pseudo type node so that it can be handled in the same way as other type node.