<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_revision():
 	""" 	Retrieve the current git revision identifier. If the git binary can not be 	found or the repository information is unavailable, None will be returned. 	:return: The git revision tag if it's available. 	:rtype: str 	"""

	git_bin = smoke_zephyr.utilities.which('git')
	if not git_bin:
		return None
	proc_h = subprocess.Popen(
		(git_bin, 'rev-parse', 'HEAD'),
		stdout=subprocess.PIPE,
		stderr=subprocess.PIPE,
		close_fds=True,
		cwd=os.path.dirname(os.path.abspath(__file__))
	)
	rev = proc_h.stdout.read().strip()
	proc_h.wait()
	if not len(rev):
		return None
	return rev.decode('utf-8')