Argument resolver crashes when omitting a nullable input field of type list

[ptrf]

The schema snippets below sets the stage

input I {
     nonNull: String!
     list: [String]
}

type Mutation {
     m(input: I!): ...
}

GraphQL crashes with runtime error {case_clause, null} in graphql_execute.erl when attempting to perform this mutation:

mutation M {
  m(input: {nonNull: "non-nullable string"}) {
    ...
  }
}

[ptrf]

If the list field of input type I has a default value, the crash doesn't happen - i.e. list: [String] = [].

[ptrf]

The bug only triggers for arguments written in the query doc. The following mutation:

mutation M($input: I!) {
  m(input: $input) {
    ...
  }
}

with variables { "input": {"nonNull": "non-nullable string"} } works fine.

[jlouis]

Fix merged, lets close this one.