input: Write a python function to handle user input for a search query, remove stopwords, and find related questions from a predefined database.
  assert search_related_questions('What is an array')=={'How do you create an empty array in Python?', 'What is an array in programming?'}
  assert search_related_questions('Python advantages')=={'What are the advantages of using Python?'}
  assert search_related_questions('What is Python')=={'What is Python?'}
output: def search_related_questions(query):
      stopwords = {'is', 'an', 'a', 'the', 'in', 'on', 'and', 'or', 'what'}
      database = {
          'How do you create an empty array in Python?',
          'What is an array in programming?',
          'What are the advantages of using Python?',
          'What is Python?'
      }
  
      # Process the query: remove stopwords and convert to lowercase
      query_words = set(query.lower().split()) - stopwords
  
      # Find related questions
      related_questions = set()
      for question in database:
          question_words = set(question.lower().split()) - stopwords
          if query_words.intersection(question_words):
              related_questions.add(question)
  
      return related_questions