input: Write a function to convert a given SQL statement into a Python Pandas DataFrame. The function should take a SQL query as input and return a Pandas DataFrame. Assume that the connection object `conn` is already established.
  assert convert_sql_to_df("SELECT * FROM book;").equals(pd.read_sql_query("SELECT * FROM book;", conn))==True
  assert convert_sql_to_df("SELECT title, author FROM book;").equals(pd.read_sql_query("SELECT title, author FROM book;", conn))==True
  assert convert_sql_to_df("SELECT * FROM customer;").equals(pd.read_sql_query("SELECT * FROM customer;", conn))==True
  assert convert_sql_to_df("").equals(pd.DataFrame())==True
  assert convert_sql_to_df("SELECT * FROM non_existent_table;").equals(pd.DataFrame())==False
output: def convert_sql_to_df(sql_query):
      if not sql_query:
          return pd.DataFrame()
      try:
          return pd.read_sql_query(sql_query, conn)
      except:
          return pd.DataFrame()