I'm getting an unexpected NullReferenceException when I run this code, omitting the fileSystemHelper parameter (and therefore defaulting it to null):
public class GitLog
{
FileSystemHelper fileSystem;
/// <summary>
/// Initializes a new instance of the <see cref="GitLog" /> class.
/// </summary>
/// <param name="pathToWorkingCopy">The path to a Git working copy.</param>
/// <param name="fileSystemHelper">A helper class that provides file system services (optional).</param>
/// <exception cref="ArgumentException">Thrown if the path is invalid.</exception>
/// <exception cref="InvalidOperationException">Thrown if there is no Git repository at the specified path.</exception>
public GitLog(string pathToWorkingCopy, FileSystemHelper fileSystemHelper = null)
{
this.fileSystem = fileSystemHelper ?? new FileSystemHelper();
string fullPath = fileSystem.GetFullPath(pathToWorkingCopy); // ArgumentException if path invalid.
if (!fileSystem.DirectoryExists(fullPath))
throw new ArgumentException("The specified working copy directory does not exist.");
GitWorkingCopyPath = pathToWorkingCopy;
string git = fileSystem.PathCombine(fullPath, ".git");
if (!fileSystem.DirectoryExists(git))
{
throw new InvalidOperationException(
"There does not appear to be a Git repository at the specified location.");
}
}
When I single step the code in the debugger, after I step over the first line (with the ?? operator) then fileSystem still has the value null, as shown in this screen snip (stepping over the next line throws NullReferenceException):
This is not what I expected! I'm expecting the null coalescing operator to spot that the parameter is null and create a new FileSystemHelper(). I have stared at this code for ages and can't see what is wrong with it.
ReSharper pointed out that the field is only used in this one method, so could potentially be converted to a local variable... so I tried that and guess what? It worked. So, I have my fix, but I cannot for the life of me see why the code above doesn't work. I feel like I am on the edge of learning something interesting about C#, either that or I've done something really dumb. Can anyone see what's happening here?
