Test for NaN correctly

System.Double.NaN, which represents a value that's not a number, results when an arithmetic operation is undefined. Any expression that tests for equality between a value and System.Double.NaN always returns false. Any expression that tests for inequality (!= in C#) between a value and System.Double.NaN always returns true.

An expression tests a value against System.Single.NaN or System.Double.NaN.

To fix a violation of this rule and accurately determine whether a value represents System.Double.NaN, use System.Single.IsNaN or System.Double.IsNaN to test the value.

Do not suppress a warning from this rule.