Wordpress error on latest_post() function - php

Question

im my single.php file I have two functions that displays related posts to the one currently reading. When I add a new post and do not add tags to it, an error will appear when I try to preview it.
Error thrown
Call to a member function have_posts () on null
When I add tags to it, everything displays fine.
<?php
//for use in the loop, list 5 post titles related to first tag on current post
$tags = wp_get_post_tags($post->ID);
if ($tags) :
$tag_ids = array();
foreach($tags as $individual_tag) $tag_ids[] = $individual_tag->term_id;
$args=array(
'tag__in' => $tag_ids,
'post__not_in' => array($post->ID),
'posts_per_page'=>6,
'caller_get_posts'=>1
);
$my_query = new WP_Query($args);
if( $my_query->have_posts() ) :
?>
<div class="d-block d-lg-none text-center" >
<?php get_sidebar(); ?>
<div class="col-12 col-lg-7 offset-lg-1">
<div id="powiazane">
<h2> Powiązane artykuły: </h2>
<div class="card-deck mb-50px">
<?php
$post_wrap = 0;
while ($my_query->have_posts()) : $my_query->the_post(); ?>
<article id="post-<?php the_ID(); ?>" <?php post_class('card border-0 ' . $termsString); ?>>
<img class="card-img-top secondary-post-img p-3" src="<?php echo the_post_thumbnail_url('post-thumb'); ?>" alt="<?php the_title_attribute(); ?>">
<div class="card-body">
<a href="<?php the_permalink(); ?>" class="stretched-link" alt="<?php the_title_attribute(); ?>">
<?php
if(get_field('tytul_krotki'))
{
echo '<h3>' . get_field('tytul_krotki') . '</h3>';
} else {
echo '<h3>' . get_the_title() . '</h3>';
}
?>
</a>
<div class="small text-muted">
<p class="mb-0">
<?php the_field('miasto'); ?> | <?php echo hubdab_relative_time(); ?>
</p>
</div>
<p class="mt-25px"><?php the_field('lid_krotki') ?> </p>
</div>
<div class="card-footer py-0">
</div>
</article><!-- #post-## -->
<?php
if ($post_wrap % 2 == 1){
echo '<div class="w-100 d-none d-sm-block"><!-- wrap every 2 on sm+--></div>';
}
$post_wrap++; ?>
<?php
endwhile;
?>

Answer 1

You have a problem in this code
$tags = wp_get_post_tags($post->ID);
if ($tags) :
$tag_ids = array();
foreach($tags as $individual_tag) $tag_ids[] = $individual_tag->term_id;
$args=array(
'tag__in' => $tag_ids,
'post__not_in' => array($post->ID),
'posts_per_page'=>6,
'caller_get_posts'=>1
);
$my_query = new WP_Query($args);
if( $my_query->have_posts() )
$tags = wp_get_post_tags($post->ID) will return
(array|WP_Error) Array of WP_Term objects on success or empty array if no tags were found. WP_Error object if 'post_tag' taxonomy doesn't exist.
So if you check for if($tags) always will be true, as WP_Error will be true in case of no tags.
You can modify your condition to execute the query as:
if (!is_wp_error($tags) and count($tags)):
....
Hope this help