| Check | Code | Description |
| Is Null | if(variable is null) return true;
| -
 This syntax supports static analysis such that later code will know whether variable is null or not. -
 Doesn’t produce a warning even when comparing against a non-nullable value type making the code to check pointless. -
 Requires C# 7.0 because it leverages type pattern matching. |
| Is Not Null | if(variable is { }) return false
| - This syntax supports static analysis such that later code will know whether variable is null or not.
- Requires C# 8.0 since this is the method for checking for not null using property pattern matching.
|
| Is Not Null | if(variable is object) return false
| - Triggers a warning when comparing a non-nullable value type which could never be null
- This syntax works with C# 8.0’s static analysis so later code will know that variable has been checked for null.
- Checks if the value not null by testing whether it is of type object. (Relies on the fact that null values are not of type object.)
|
| Is Null | if(variable == null) return true
| - The only way to check for null prior to C# 7.0.
- However, because the equality operator can be overridden, this has the (remote) possibility of failing or introducing a performance issue.
|
| Is Not Null | if(variable != null) return false
| - The only way to check for not null prior to C# 7.0.
- Since the not-equal operator can be overridden, this has the (remote) possibility of failing or introducing a performance issue.
|
