"Add null check" results in incorrect null check

[mjcheetham]

Version information

Product	Version
Refactoring Essentials VSIX	4.8.0.0
Visual Studio	2015 Community (Update 3)

Description

The "Add null check" refactoring applied to member access does not ensure the added null check is performed in the correct order in an existing if condition expression. The x.y.z != null expression should occur after both x and x.y have been null-checked.

Example code

Press Ctrl + . with cursor at the member access on foo and apply the "Add null check" refactoring..

if (foo != null)
{
    returnValue = foo.Bar.Value;
}

..becomes..

// If foo is null then the expression "foo.Bar != null" will cause a NullReferenceException
if ((foo.Bar != null) && (foo != null))
{
    returnValue = foo.Bar.Value;
}

..whereas it should be..

// foo should be null-checked before an expression containing a member access of foo
if ((foo != null) && (foo.Bar != null))
{
    returnValue = foo.Bar.Value;
}