Fix forms input placeholder displaying when its value is "0" (#42173)

* Fix forms input placeholder displaying when its value is "0"

* changelog

* Check if placeholder is null

Committed via a GitHub action: https://github.com/Automattic/jetpack/actions/runs/14026333964

Upstream-Ref: Automattic/jetpack@9ab420d

Author: tellthemachines

CHANGELOG.md

@@ -15,6 +15,7 @@ This is an alpha version! The changes listed here are not final.
 
 ### Fixed
 - Components: Add __next40pxDefaultSize to controls, preventing deprecation notices.
+- Placeholder should always display if it's a non-empty string
 
 ## [0.43.0] - 2025-03-18
 ### Added

src/contact-form/class-contact-form-field.php

@@ -1066,14 +1066,14 @@ public function render_field( $type, $id, $label, $value, $class, $placeholder,
 
 		$form_style = $this->get_form_style();
 		if ( ! empty( $form_style ) && $form_style !== 'default' ) {
-			if ( empty( $placeholder ) ) {
+			if ( ! isset( $placeholder ) || '' === $placeholder ) {
 				$placeholder .= ' ';
 			} else {
 				$class .= ' has-placeholder';
 			}
 		}
 
-		$field_placeholder = ( ! empty( $placeholder ) ) ? "placeholder='" . esc_attr( $placeholder ) . "'" : '';
+		$field_placeholder = ( '' !== $placeholder ) ? "placeholder='" . esc_attr( $placeholder ) . "'" : '';
 		$field_class       = "class='" . trim( esc_attr( $type ) . ' ' . esc_attr( $class ) ) . "' ";
 		$wrap_classes      = empty( $class ) ? '' : implode( '-wrap ', array_filter( explode( ' ', $class ) ) ) . '-wrap'; // this adds
 		$has_inset_label   = $this->has_inset_label();