Error when explicit null provided for nullable list input parameter

[ajawalker]

Description

When an input parameter type is a nullable list, providing an explicit value of null as the argument for that parameter generates an error.

To Reproduce

In Cargo.toml: juniper = "0.15.9"

Query object:

pub struct Query;

#[graphql_object]
impl Query {
    fn test(input: Option<Vec<i32>>) -> Option<Vec<i32>> {
        input
    }
}

This query:

query {
  test(input:null)
}

Returns this error:

{
  "errors": [
    {
      "message": "Invalid value for argument \"input\", expected type \"[Int!]\"",
      "locations": [
        {
          "line": 2,
          "column": 14
        }
      ]
    }
  ]
}

Providing an explicit value or providing no value (an implicit null) both produce the expected result. Also, an explicit null value works for other nullable types, just not nullable list types.

Expected behavior

Providing an explicit null argument for a nullable list parameter should not produce an error, but should behave exactly the same as an implicit null for Option<Vec<_>> types, or become the ImplicitNull variant for Nullable<Vec<_>> types.

[ajawalker]

Addressed by #1086

[tyranron]

Released in 0.15.10.