According to the Graphql language Spec it is allowed to provide a non-list as a value for the list type inputs. According to the spec, if the value's type matches the list item type, the value is interpreted as a singleton list.

While it works in queries, it does not work in schemas, in particular in schema directives with the arguments of List Type.
For example the following fragment of a schema produces the error below:

directive @test( value: [String] ) on FIELD_DEFINITION
type TestType {
testField: Int @test(value: "some value")
}

Error: 'testField' [@47:5] uses an illegal value for the argument 'value' on directive 'test'. Argument value is 'StringValue', expected a list value