It is common to want to check an object against null, but this should not be done using the Equals method. If the object really is null, a NullReferenceException is thrown when attempting to call Equals, with unexpected results.

The offending call should be replaced with either == or ReferenceEquals (the difference being that == can be overridden but ReferenceEquals cannot).

In the following example, IsNull will throw a NullReferenceException when o is null.

In the revised example, IsNull will correctly return true when o is null.

MSDN: Object.Equals Method (Object).