Unification of int, empty array and int array fails

[asterite]

a = 1
a = []
a = []
a << 1

"a" is incorrectly typed as a union of Int and Array<Int>, but it should be a union of Int, Array<Nil> and Array<Int>

[asterite]

Simpler test case:

class Int
  def value=(x)
  end
end

a = 1
a = Pointer.malloc(1)
a.value = 1
a = Pointer.malloc(1)

It's simpler because it doesn't involve arrays.

And another one with just objects:

generic class Foo
  def value=(value)
    @value = value
  end
end

foo = Foo.new
foo.value = 1
foo = Foo.new

Should be union of Foo<> and Foo<Int> but it's just Foo<Int>