# Buggy code
def checkout_exp(self, rev, allow_missing=False):
    """Checkout an experiment to the user's workspace."""
    from git.exc import GitCommandError

    from dvc.repo.checkout import checkout as dvc_checkout

    baseline_rev = self._check_baseline(rev)
    self._scm_checkout(rev)

    tmp = tempfile.NamedTemporaryFile(delete=False).name
    self.scm.repo.head.commit.diff(
        baseline_rev, patch=True, full_index=True, binary=True, output=tmp
    )

    dirty = self.repo.scm.is_dirty()
    if dirty:
        logger.debug("Stashing workspace changes.")
        self.repo.scm.repo.git.stash("push", "--include-untracked")

    try:
        if os.path.getsize(tmp):
            logger.debug("Patching local workspace")
            self.repo.scm.repo.git.apply(tmp, reverse=True)
            need_checkout = True
        else:
            need_checkout = False
    except GitCommandError:
        raise DvcException("failed to apply experiment changes.")
    finally:
        remove(tmp)
        if dirty:
            self._unstash_workspace()

    if need_checkout:
        dvc_checkout(self.repo, allow_missing=allow_missing)


# Traceback (git.exc.GitCommandError)
❯ dvc exp run --continue -v
...
2020-10-23 16:36:29,034 DEBUG: Commit to current experiment branch
2020-10-23 16:36:29,118 DEBUG: Checking out experiment commit 'd5dbcff520d30b5d92a863049f7259044a145a28'
2020-10-23 16:36:29,148 DEBUG: Patching local workspace
2020-10-23 16:36:29,154 DEBUG: Removing '/var/folders/s_/j8cg24s945dcvlh77c677f080000gn/T/tmpj3mfqijf'
2020-10-23 16:36:29,155 DEBUG: fetched: [(60,)]
2020-10-23 16:36:29,156 ERROR: failed to apply experiment changes.
------------------------------------------------------------
Traceback (most recent call last):
File "/Users/pmrowla/git/dvc/dvc/repo/experiments/__init__.py", line 770, in checkout_exp
self.repo.scm.repo.git.apply(tmp, reverse=True)
File "/Users/pmrowla/.virtualenvs/dvc/lib/python3.8/site-packages/git/cmd.py", line 542, in <lambda>
return lambda *args, **kwargs: self._call_process(name, *args, **kwargs)
File "/Users/pmrowla/.virtualenvs/dvc/lib/python3.8/site-packages/git/cmd.py", line 1005, in _call_process
return self.execute(call, **exec_kwargs)
File "/Users/pmrowla/.virtualenvs/dvc/lib/python3.8/site-packages/git/cmd.py", line 822, in execute
raise GitCommandError(command, status, stderr_value, stdout_value)
git.exc.GitCommandError: Cmd('git') failed due to: exit code(1)
cmdline: git apply --reverse /var/folders/s_/j8cg24s945dcvlh77c677f080000gn/T/tmpj3mfqijf
stderr: 'error: dvc.lock: already exists in working directory'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/Users/pmrowla/git/dvc/dvc/command/experiments.py", line 456, in run
self.repo.experiments.run(
File "/Users/pmrowla/git/dvc/dvc/repo/experiments/__init__.py", line 881, in run
return run(self.repo, *args, **kwargs)
File "/Users/pmrowla/git/dvc/dvc/repo/__init__.py", line 51, in wrapper
return f(repo, *args, **kwargs)
File "/Users/pmrowla/git/dvc/dvc/repo/experiments/run.py", line 62, in run
return repo.experiments.reproduce_one(
File "/Users/pmrowla/git/dvc/dvc/repo/experiments/__init__.py", line 398, in reproduce_one
self.checkout_exp(exp_rev, allow_missing=checkpoint)
File "/Users/pmrowla/git/dvc/dvc/repo/experiments/__init__.py", line 38, in wrapper
return f(exp, *args, **kwargs)
File "/Users/pmrowla/git/dvc/dvc/repo/experiments/__init__.py", line 775, in checkout_exp
raise DvcException("failed to apply experiment changes.")
dvc.exceptions.DvcException: failed to apply experiment changes.
------------------------------------------------------------

# Fixed code
def checkout_exp(self, rev, **kwargs):
    """Checkout an experiment to the user's workspace."""
    from git.exc import GitCommandError

    from dvc.repo.checkout import checkout as dvc_checkout

    baseline_rev = self._check_baseline(rev)
    self._scm_checkout(rev)

    branch = self._get_branch_containing(rev)
    m = self.BRANCH_RE.match(branch)
    if m and m.group("checkpoint"):
        kwargs.update({"allow_missing": True, "quiet": True})

    tmp = tempfile.NamedTemporaryFile(delete=False).name
    self.scm.repo.head.commit.diff(
        baseline_rev, patch=True, full_index=True, binary=True, output=tmp
    )

    dirty = self.repo.scm.is_dirty(untracked_files=True)
    if dirty:
        logger.debug("Stashing workspace changes.")
        self.repo.scm.repo.git.stash("push", "--include-untracked")

    try:
        if os.path.getsize(tmp):
            logger.debug("Patching local workspace")
            self.repo.scm.repo.git.apply(tmp, reverse=True)
            need_checkout = True
        else:
            need_checkout = False
    except GitCommandError:
        raise DvcException("failed to apply experiment changes.")
    finally:
        remove(tmp)
        if dirty:
            self._unstash_workspace()

    if need_checkout:
        dvc_checkout(self.repo, **kwargs)