php error using wordpress function get_terms - php

Question

I'm setting a variable in my site this way:
$args = array('parent' => 2818,'hide_empty' => false);
$best_of_cat_child_terms = get_terms( $args ); -> (functions.php:26)
$best_of_cat = $best_of_cat_child_terms;
The problem is that I'm also getting this php error:
Warning:
Invalid argument supplied for foreach()
Location:
wp-includes/class-wp-term-query.php:373
Call Stack:
WP_Term_Query->get_terms()
wp-includes/class-wp-term-query.php:287
WP_Term_Query->query()
wp-includes/taxonomy.php:1217
get_terms()
wp-content/themes/theme-child/functions.php:26 (-> functions.php line 26 marked above)
Am I setting this the right way?

Answer 1

You can check for the error with is_wp_error(),
$terms = get_terms( array(
'taxonomy'=> 'category',
'parent' => 2818,
'hide_empty' => 0)
);
if ( ! empty( $terms ) && ! is_wp_error( $terms ) ){
echo '<ul>';
foreach ( $terms as $term ) {
echo '<li>' . $term->name . '</li>';
}
echo '</ul>';
}
else{
$error_string = $terms->get_error_message();
echo '<div id="message" class="error"><p>' . $error_string .'</p></div>';
}
About the error you told in comment, it's look like you don't run with a WordPress version under 4.5 ?
Prior to 4.5.0, the first parameter of get_terms() was a taxonomy or list of taxonomies:
$terms = get_terms( 'post_tag', array(
'hide_empty' => false,
) );
Since 4.5.0, taxonomies should be passed via the ‘taxonomy’ argument in the $args array:
$terms = get_terms( array(
'taxonomy' => 'post_tag',
'hide_empty' => false,
) );
About get_terms()
In your case, remove taxonomy from $args and
$terms = get_terms('category', $args);

Answer 2

Provide the taxonomy arg:
$args = array(
'taxonomy' => 'your_taxonomy',
'parent' => 2818,
'hide_empty' => false
);