input: Write a function that converts a given SQL statement into a Python Pandas DataFrame. The function should take a SQL query as input and return a Pandas DataFrame. If the SQL query is invalid, the function should return an empty DataFrame.
  assert convert_sql_to_df("SELECT * FROM book;")==pd.DataFrame()
  assert convert_sql_to_df("SELECT id, title FROM books")==pd.DataFrame()
  assert convert_sql_to_df("SELECT * FROM authors;")==pd.DataFrame()
  assert convert_sql_to_df("SELECT name, age FROM users")==pd.DataFrame()
  assert convert_sql_to_df("")==pd.DataFrame()
output: def convert_sql_to_df(sql_query):
      try:
          import pandas as pd
          import sqlite3
          conn = sqlite3.connect(':memory:')
          df = pd.read_sql_query(sql_query, conn)
          conn.close()
          return df
      except:
          return pd.DataFrame()