validation allows `null` for non-nullable list items

[qwerdenkerXD]

Description

When having arguments of type List with non-nullable items, such as e.g. [String!], the validation doesn't recognize a violation if I pass a list with null-values.

Steps to reproduce

Imagine having this schema:

type Query {
  foo(arg: [String!]!): String!
  bar(arg: [String!]): String!
}

and validating the following query:

{
  a: foo(arg: [null])
  b: foo(arg: [null, null, "hello"])
  bar(arg: [null])
}

Here a code sample.

Expected result

The validation should identify the violation and append it to the diagnostic list.

Actual result

The validation doesn't notice the violation, no such error in diagnostics. (also in version 0.11.3)

Environment

• Operating system and version: Ubuntu 20.04.6 LTS
• Shell (bash/zsh/powershell): zsh
• apollo-rs crate: apollo-compiler
• Crate version: 1.0.0-beta.6

[qwerdenkerXD]

Just checked it for input objects, same issue if an input object field expects such list type.