Type checker fails to prevent nullable value from being assigned to array/dictionary which is typed to have non-nullable values

But the type checker is able to prevent null from being assigned in the same cases. And it is able to prevent a nullable value from being assigned to a scalar variable (not array/dictionary member) which is typed to be non-nullable.

- SDK 8.1.1

- type check level: 1, 2 or 3

import Toybox.Lang;

var floatVal as Float = 42.0;
var floatArray as Array<Float> = [ 42.0 ];
var floatDictionary as Dictionary<String, Float> = {} as Dictionary<String, Float>;

function bar(x as Float?) as Void {
    floatVal = null; // ✅ ERROR: fr955: Cannot assign value 'Null' to member ':floatVal'.
    floatVal = x; // ✅ ERROR: fr955: Assigned value type 'PolyType<Null or $.Toybox.Lang.Float>' to member '$.floatVal' of non-poly type '$.Toybox.Lang.Float'.

    floatArray[0] = null; // ✅ ERROR: fr955: Cannot assign type 'Null' to '$.Toybox.Lang.Array<$.Toybox.Lang.Float>'.
    floatArray[0] = x; // ❌ no error

    floatDictionary["foo"] = null; // ✅ ERROR: fr955: Cannot assign type 'Null' to '$.Toybox.Lang.Dictionary<$.Toybox.Lang.String,$.Toybox.Lang.Float>'.
    floatDictionary["foo"] = x; // ❌ no error
}

Expected behaviour:

- every line in bar() should have an error related to assigning a null / nullable value to something which isn't nullable

Notes:

- the type checker clearly knows that x is a Float or Null as per the error when trying to assign it to floatVal, and as per the type information that appears when you hover over any instance of x:

> var x as $.Toybox.Lang.Float or Null

- as per the comment below, the general issue seems to be that the checker only ensures that at least one type of a given polytype is valid when it's assigned to an element of an array/dictionary, while it should check that all types are valid.