input: Write a function to convert a given SQL statement into a Pandas DataFrame. The function should take the SQL statement as a string and a SQL connection object as input. It should return the resulting DataFrame. Use the `pandas.read_sql_query` function to execute the SQL query.
  
  def sql_to_dataframe(sql_statement: str, conn) -> pd.DataFrame:
      return pd.read_sql_query(sql_statement, conn)
  
  assert sql_to_dataframe("SELECT * FROM book;", conn).equals(pd.read_sql_query("SELECT * FROM book;", conn))
  assert sql_to_dataframe("SELECT title, author FROM book;", conn).equals(pd.read_sql_query("SELECT title, author FROM book;", conn))
  assert sql_to_dataframe("", conn).equals(pd.DataFrame())
  assert sql_to_dataframe("SELECT * FROM nonexistent_table;", conn).equals(pd.DataFrame())
output: def sql_to_dataframe(sql_statement: str, conn) -> pd.DataFrame:
      if sql_statement.strip() == "":
          return pd.DataFrame()
      try:
          return pd.read_sql_query(sql_statement, conn)
      except:
          return pd.DataFrame()