[WordPress] A strategy for saving post meta data when there's only actual data to save, and retrieving the information only if there's something to retrieve.

1-acme-save-post-meta-data.php

<?php

add_action( 'save_post', 'acme_save_post_meta_data' );
/**
 * Saves the incoming $_POST data to the post meta data (with the post
 * identified by the incoming ID) if and only if the value of the
 * data isn't empty.
 * 
 * Authorisation, authentication and sanitization omitted for brevity.
 * 
 * @param    int    $post_id    The associated post ID
 */
function acme_save_post_meta_data( $post_id ) {
  
  $meta_value = $_POST['post-key'];
  
  if ( isset( $meta_value ) ) {
    add_post_meta( $post_id, 'acme_post_meta_key', $meta_value );
  }
  
}

2-acme-save-post-meta-data.php

<?php

add_action( 'save_post', 'acme_save_post_meta_data' );
/**
 * Saves the incoming $_POST data to the post meta data (with the post
 * identified by the incoming ID) if and only if the value of the
 * data isn't empty.
 * 
 * Authorisation, authentication and sanitization omitted for brevity.
 * 
 * @param    int    $post_id    The associated post ID
 */
function acme_save_post_meta_data( $post_id ) {
  
  $meta_value = $_POST['post-key'];
  
  if ( isset( $meta_value ) && 0 < strlen( trim( $meta_value ) ) ) {
    add_post_meta( $post_id, 'acme_post_meta_key', $meta_value );
  }
  
}

3-acme-get-post-meta-data.php

<?php

/**
 * Retrieving the meta data associated with the 'acme_post_meta' key for
 * the specified $post_id.
 * 
 * If no value is found, then null will be returned.
 * 
 * @param    int    $post_id    The associated post ID
 * @return                      The value; otherwise, null
 */
function acme_get_post_meta_data( $post_id ) {
  
  $value = get_post_meta( $post_id, 'acme_post_meta_key', false );
  return empty( $value ) ? null : $value;
  
}