input: Write a function to create a web application in Python using Flask that takes user input and generates an HTML page displaying the input. The function should start the Flask application. If successful, the output should be an HTML page displaying the user input. If the input is empty, the page should display "No input provided".
  assert create_flask_app('Hello World!') == None  # Application should start and display "Hello World!" on the webpage
  assert create_flask_app('') == None  # Application should start and display "No input provided" on the webpage
  assert create_flask_app(None) == None  # Application should start and display "No input provided" on the webpage
output: from flask import Flask, request, render_template_string
  
  def create_flask_app(input_text):
      app = Flask(__name__)
  
      @app.route('/')
      def index():
          if input_text:
              return render_template_string('<h1>{{ input_text }}</h1>', input_text=input_text)
          else:
              return 'No input provided'
  
      app.run()