Why is [CanBeNull] appended to IEquatable<T>.Equals() of struct? Is it an error?

public struct Student : IEquatable<Student>
{
    public int StudentNumber { get; }

    public Student(int studentNumber)
    {
        StudentNumber = studentNumber;
    }

    public bool Equals([CanBeNull]Student other)
    {
        return StudentNumber == other.StudentNumber;
    }
}

public class Program
{
    private void Operation()
    {
        var student = new Student(1234);
        var result = student.Equals(obj: null);
    }
}

Tags shown in Rider(2021.3.4v) are shown in bold italics.

student.Equals(null) executes Equals() of ValueType. That is, Student's Equals() method cannot be null.

Is it an error to say this in the IDE? Or am I misunderstood?