input: from typing import List, Optional
  
  def find_customer(customers: List[str], query: str) -> Optional[str]:
      """
      Searches for a customer in the list of known customers by name and returns the customer's name if found.
      Returns None if the customer is not found.
      >>> find_customer(["John Doe", "Jane Smith", "Alice Johnson"], "Jane Smith")
      'Jane Smith'
      >>> find_customer(["John Doe", "Jane Smith", "Alice Johnson"], "Bob Brown")
      None
      """
      for customer in customers:
          if customer == query:
              return customer
      return None
output:     for customer in customers:
          if customer == query:
              return customer
      return None