Which is the equivalent of git checkout branch_name on LibGit2Sharp

I have 2 branches in git server which are master and development. I am cloning a repository to my machine using the following code.

var options =
    new CloneOptions()
    {
        CredentialsProvider = this.credentialsHandler,
    };

return
    Repository.Clone(
        gitHttpUrl,
        localPath,
        options);

      

        
        
        
      

    

The default split is master. I want to switch to developing a branch with the following code.

using (var repo = new Repository(localPath))
{
    var branch = repo.Branches[branchName];

    repo.Checkout(branch);
}

      

        
        
        
      

    

but the branch is null.

How can I switch a branch using LibGit2Sharp?

Update
Separation by default master

and below are the steps to reproduce the problem.

• Trailed
• Checkout develop
  
  branch
• Pull, an exception is thrown here.

This is the code:

private void Checkout(string localPath, string branchName)
{
    using (var repo = new Repository(localPath))
    {
        var branch = repo.Branches[branchName];

        if (branch == null)
        {
            branch = repo.CreateBranch(branchName, "origin/" + branchName);
        }

        repo.Checkout(branch);
    }
}

private MergeResult Pull(string path)
{
    const string NAME = "test-user";
    const string EMAIL = "test-email@gmail.com";

    using (var repo = new Repository(path))
    {
        var merger =
            new Signature(
                NAME,
                EMAIL,
                DateTimeOffset.UtcNow);

        var options =
            new PullOptions
            {
                FetchOptions = new FetchOptions()
                {
                    CredentialsProvider = this.credentialsHandler
                }
            };

        return repo.Network.Pull(merger, options);
    }
}