V3042. Possible NullReferenceException. The '?.' and '.' operators are used for accessing members of the same object.

The analyzer has detected that members of one object are accessed in two different ways – using operators "?." and ".". When accessing a part of an expression through "?.", it is assumed that the preceding member may be null; therefore, trying to access this member using operator "." will cause a crash.

Consider the following example:

if (A?.X == X || A.X == maxX)
...

The programmer's inattention may result in a situation when the first check will return false and the second check will raise a NullReferenceException if "A" is null. The fixed code should look like this:

if (A?.X == X || A?.X == maxX)
...

And here is another example of this error, taken from a real application:

return node.IsKind(SyntaxKind.IdentifierName) && 
       node?.Parent?.FirstAncestorOrSelf<....>() != null;

In the second part of the condition, it is assumed that "node" may be null: "node?.Parent"; but there is no such check when calling function "IsKind".

This diagnostic is classified as: