Nullable interface fields cannot have their implementing sub-type be non-nullable.

[nickdichev]

Environment

• Elixir version (elixir -v): Elixir 1.11.1 (compiled with Erlang/OTP 23)
• Absinthe version (mix deps | grep absinthe): absinthe 1.5.3 (Hex package) (mix)
• Client Framework and version (Relay, Apollo, etc): N/A getting compilation error

Expected behavior

The schema compiles and the implementing sub-type is valid.

Actual behavior

Compilation error

Type "header_cell" does not fully implement interface type "manifest_cell" for fields [:text]
...
  * An object field type is a valid sub-type if it is a Non-Null variant of a
    valid sub-type of the interface field type.

Relevant Schema/Middleware Code

  interface :manifest_cell do
    field :text, :string
  end

  object :header_cell do
    field :text, non_null(:string)

    interface :manifest_cell
    is_type_of &is_struct(&1, HeaderCell)
  end