Nullability of reference types in type of parameter 'obj' of 'int DecreasingNumberSequence.CompareTo(object obj)' doesn't match implicitly implemented member 'int IComparable.CompareTo(object? obj)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'other' of 'bool DigitalAction.Equals(IAction other)' doesn't match implicitly implemented member 'bool IEquatable<IAction>.Equals(IAction other)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'other' of 'bool DummyAction.Equals(IAction other)' doesn't match implicitly implemented member 'bool IEquatable<IAction>.Equals(IAction other)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'other' of 'bool LambdaAction.Equals(IAction other)' doesn't match implicitly implemented member 'bool IEquatable<IAction>.Equals(IAction other)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'other' of 'bool BinaryAction.Equals(IAction other)' doesn't match implicitly implemented member 'bool IEquatable<IAction>.Equals(IAction other)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'other' of 'bool AnyAction.Equals(IAction other)' doesn't match implicitly implemented member 'bool IEquatable<IAction>.Equals(IAction other)' (possibly because of nullability attributes).

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.

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

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.