input: Write a function that creates a Python web application for a car insurance calculator. The application should have a page where the user can input the data (e.g., age, gender, car model, etc.) and return a calculated insurance price. The function should set up the Flask application, define a route to handle the calculation, and return the insurance price in JSON format. If the input data is missing, handle it appropriately.
  
  assert app.calculate({'age': 30, 'gender': 'male', 'car_model': 'Ford'})=={'insurance_price': 0.00}
  assert app.calculate({'age': 25, 'gender': 'female', 'car_model': 'Toyota'})=={'insurance_price': 0.00}
  assert app.calculate({'age': 40, 'gender': 'male', 'car_model': 'Honda'})=={'insurance_price': 0.00}
  assert app.calculate({'age': 22, 'gender': 'female', 'car_model': 'Chevrolet'})=={'insurance_price': 0.00}
output: 
  def calculate(data):
      required_fields = ['age', 'gender', 'car_model']
      for field in required_fields:
          if field not in data:
              return {'error': f'Missing required field: {field}'}
      
      # Placeholder calculation for insurance price
      insurance_price = 0.00
      
      return {'insurance_price': insurance_price}
  