// I have this code in my single.php file and i am trying to reduce duplication
// code is under below, this code works for me but this is displaying multiple //messages to me such as
/*
Notice: Trying to access array offset on value of type null in C:xampphtdocswp-vs-5.3.2wp-contentthemespersonalfunctions.php on line 4

Notice: Undefined index: subtitle in C:xampphtdocswp-vs-5.3.2wp-contentthemespersonalfunctions.php on line 7

Notice: Undefined index: photo in C:xampphtdocswp-vs-5.3.2wp-contentthemespersonalfunctions.php on line 10
*/

// SINGLE.PHP File
while (have_posts() ) {
    the_post();   
  site_banner_section();
  ?>

// FUNCTIONS.PHP File

<?php

function site_banner_section($args = null) {
  if (!$args['title']) {
    $args['title'] = get_the_title();
  }
  if (!$args['subtitle']) {
    $args['subtitle'] = get_field('page_banner_subtitle');
  }
  if (!$args['photo']) {
    if (get_field('page_banner_background_image')) {
      $args['photo']= get_field('page_banner_background_image')['sizes']['bannerImage'];
    }else{
      $args['photo']=get_theme_file_uri('/images/ocean.jpg');
    }
  }
  ?>
  <div class="page-banner">
  <div class="page-banner__bg-image" style="background-image: url(<?php echo $args['photo']; ?>);"></div>
  <div class="page-banner__content container container--narrow">
    <h1 class="page-banner__title"><?php echo $args['title']; ?></h1>
    <div class="page-banner__intro">
      <p><?php echo $args['subtitle']; ?></p>
    </div>
  </div>
</div>

<?php