Instantiation of all UsernamePasswordCredentials ensure non-null password.

It also supports null/empty password, but guards against passing null to
libgit2sharp.

This is to avoid runtime errors when using personal access tokens to authenticate
when fetching etc. from private github repos.

The standard way to authenticate:

new UsernamePasswordCredentials
{
    Username = "<github-personal-access-token>", // GITVERSION_REMOTE_USERNAME
    Password = string.Empty
};

GitVersion should support this authentication scheme necessary when having 2FA.

When using environment variables to propagate credentials password will end up
being null, because GITVERSION_REMOTE_PASSWORD is not present when passing empty
value.

This commit guards against libgit2sharp throwing LibGit2SharpException:
"UsernamePasswordCredentials contains a null Username or Password."

Author: maxild

src/GitVersionCore/Core/GitPreparer.cs

@@ -149,14 +149,14 @@ private void CloneRepository(string repositoryUrl, string gitDirectory, Authenti
 
             if (auth != null)
             {
-                if (!string.IsNullOrWhiteSpace(auth.Username) && !string.IsNullOrWhiteSpace(auth.Password))
+                if (!string.IsNullOrWhiteSpace(auth.Username))
                 {
                     log.Info($"Setting up credentials using name '{auth.Username}'");
 
                     credentials = new UsernamePasswordCredentials
                     {
                         Username = auth.Username,
-                        Password = auth.Password
+                        Password = auth.Password ?? string.Empty
                     };
                 }
             }

src/GitVersionCore/Extensions/RepositoryExtensions.cs

@@ -196,7 +196,7 @@ private static IEnumerable<DirectReference> GetRemoteTipsUsingUsernamePasswordCr
             return repository.Network.ListReferences(remote, (url, fromUrl, types) => new UsernamePasswordCredentials
             {
                 Username = username,
-                Password = password
+                Password = password ?? string.Empty
             }).Select(r => r.ResolveToDirectReference());
         }
 

src/GitVersionCore/Model/AuthenticationInfo.cs

@@ -17,7 +17,7 @@ public FetchOptions ToFetchOptions()
                 fetchOptions.CredentialsProvider = (url, user, types) => new UsernamePasswordCredentials
                 {
                     Username = Username,
-                    Password = Password
+                    Password = Password ?? string.Empty
                 };
             }