CalDateTime equality operators handle null-values incorrectly.

[minichma]

CalDateTime.operator == and CalDateTime.operator != fail when comparing against null. This implies, that natural expressions like ((x == null) || (x <= y)) fail. This certainly violates the intended contract for == and !=. It probably should be implemented similar to:

public static bool operator ==(CalDateTime left, IDateTime right) => 
    (ReferenceEquals(left, null) || ReferenceEquals(right, null))
    ? ReferenceEquals(left, right):
    left.Equals(right);

public static bool operator !=(CalDateTime left, IDateTime right) =>
    (ReferenceEquals(left, null) || ReferenceEquals(right, null))
    ? !ReferenceEquals(left, right) :
    !left.Equals(right);

Other comparison operators should probably handle null values gracefully too. Here is, how Nullable<T> does it:

When you perform comparisons with nullable types, if the value of one of the nullable types is null and the other is not, all comparisons evaluate to false except for != (not equal).

[rianjs]

Looks reasonable. I’ll merge a stylistically tweaked version of this this week.

[rianjs]

Available in nuget version 4.1.5:
https://www.nuget.org/packages/Ical.Net/4.1.5