Nullability of type of parameter 'obj' doesn't match overridden member (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'other' of 'int CComboVoice.CompareTo(CComboVoice other)' doesn't match implicitly implemented member 'int IComparable<CComboVoice>.CompareTo(CComboVoice? other)' (possibly because of nullability attributes).

Cannot convert null literal to non-nullable reference type.

Nullability of reference types in type of parameter 'other' of 'int CChip.CompareTo(CChip other)' doesn't match implicitly implemented member 'int IComparable<CChip>.CompareTo(CChip? other)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'n1' of 'int C曲リストノードComparerタイトル.Compare(C曲リストノード n1, C曲リストノード n2)' doesn't match implicitly implemented member 'int IComparer<C曲リストノード>.Compare(C曲リストノード? x, C曲リストノード? y)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'n1' of 'int C曲リストノードComparer絶対パス.Compare(C曲リストノード n1, C曲リストノード n2)' doesn't match implicitly implemented member 'int IComparer<C曲リストノード>.Compare(C曲リストノード? x, C曲リストノード? y)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'n2' of 'int C曲リストノードComparerタイトル.Compare(C曲リストノード n1, C曲リストノード n2)' doesn't match implicitly implemented member 'int IComparer<C曲リストノード>.Compare(C曲リストノード? x, C曲リストノード? y)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'n2' of 'int C曲リストノードComparer絶対パス.Compare(C曲リストノード n1, C曲リストノード n2)' doesn't match implicitly implemented member 'int IComparer<C曲リストノード>.Compare(C曲リストノード? x, C曲リストノード? y)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'x' of 'int C曲リストノードComparerNodeType.Compare(C曲リストノード x, C曲リストノード y)' doesn't match implicitly implemented member 'int IComparer<C曲リストノード>.Compare(C曲リストノード? x, C曲リストノード? y)' (possibly because of nullability attributes).