get_the_post_thumbnail () não retorna nada?

Aqui está o meu código:

function widget($args, $options) { extract($args); global $post; $post_type = $options['post_type']; $num_of_posts = $options['limit']; // Create a new instance $second_query = new WP_Query( array( 'post_type' => "$post_type", 'posts_per_page' => "$num_of_posts", 'post_status' => 'publish', ) ); // The Loop if ($second_query->have_posts()) : while( $second_query->have_posts() ) : $second_query->the_post(); $content .= '' . get_the_title($post->ID) . ''; $content .= '
' .get_the_post_thumbnail($post->ID, array(290,290)). '
'; $content .= '

' . get_the_excerpt() . '

'; endwhile; else : $content = '

No ' . $options['post_type'] . 's found.

'; endif; wp_reset_postdata(); $title = "

" . $options['title'] . "

"; echo $before_widget.$title.$content.$after_widget; }

Tudo exibe bem, exceto a miniatura: – \

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