Possible null reference return.

Dereference of a possibly null reference.

Non-nullable field 'Root' must contain a non-null value when exiting constructor. Consider declaring the field as nullable.

The type 'TKey' cannot be used as type parameter 'TKey' in the generic type or method 'Dictionary<TKey, TValue>'. Nullability of type argument 'TKey' doesn't match 'notnull' constraint.

Converting null literal or possible null value to non-nullable type.

Dereference of a possibly null reference.

Converting null literal or possible null value to non-nullable type.

Dereference of a possibly null reference.

Converting null literal or possible null value to non-nullable type.