input: Write a function to create a virtual assistant using Python and Dialogflow to answer a basic set of questions. The function should take a project ID as input and continuously prompt the user for input, forwarding the input to Dialogflow for processing and printing the assistant's response. If the input is 'exit', the function should terminate. If no input is provided, the function should print a default response. The project ID should be configurable through a function argument.
  
  import dialogflow_v2 as dialogflow
  import requests
  
  def create_virtual_assistant(project_id):
      session_client = dialogflow.SessionsClient()
      session = session_client.session_path(project_id, 'session-id')
  
      while True:
          text = input('User: ')
          if text.lower() == 'exit':
              break
          if not text:
              print('Assistant: No input provided. Please ask a question.')
              continue
          
          text_input = dialogflow.types.TextInput(text=text, language_code='en-US')
          query_input = dialogflow.types.QueryInput(text=text_input)
          response = session_client.detect_intent(session=session, query_input=query_input)
  
          print('Assistant:', response.query_result.fulfillment_text)
  
  assert create_virtual_assistant('project-id')
  assert create_virtual_assistant('another-project-id')
  assert create_virtual_assistant('')
  
  print('All assertions passed.')
output: def create_virtual_assistant(project_id):
      session_client = dialogflow.SessionsClient()
      session = session_client.session_path(project_id, 'session-id')
  
      while True:
          text = input('User: ')
          if text.lower() == 'exit':
              break
          if not text:
              print('Assistant: No input provided. Please ask a question.')
              continue
          
          text_input = dialogflow.types.TextInput(text=text, language_code='en-US')
          query_input = dialogflow.types.QueryInput(text=text_input)
          response = session_client.detect_intent(session=session, query_input=query_input)
  
          print('Assistant:', response.query_result.fulfillment_text)