input: Write a function to convert a given SQL statement into a Python Pandas DataFrame using the `pandas.read_sql_query` function. The SQL statement should be provided as a string, and the function should return the resulting DataFrame. If the provided SQL statement is invalid or raises an error, the function should return an empty DataFrame.
  assert conv_sql_to_df('SELECT * FROM book;') == pd.DataFrame()
  assert conv_sql_to_df('SELECT title, author FROM book;') == pd.DataFrame()
  assert conv_sql_to_df('SELECT * FROM invalid_table;') == pd.DataFrame()
  assert conv_sql_to_df('') == pd.DataFrame()
output: def conv_sql_to_df(sql_query):
      try:
          import pandas as pd
          return pd.read_sql_query(sql_query)
      except:
          return pd.DataFrame()