from datetime import datetime


def create_timestamp(timestamp):
    """Takes a timestamp and checks if it matches pattern.

    Args:
        timestamp: (str) given timestamp

    Returns:
        str: timestamp or None if not matches pattern
    """
    try:
        datetime.strptime(timestamp, "%Y-%m-%dT%H:%M:%S.%fZ")
        return timestamp
    except ValueError:
        return None