Code Modernisation: Fix known instances of array access on data types that can't be accessed as arrays.

PHP 7.4 addes a warning when trying access a null/bool/int/float/resource (everything but array, string and object) as if it were an array.

This change fixes all of these warnings visible in unit tests.

Props jrf.
See #47704.



Built from https://develop.svn.wordpress.org/trunk@45639


git-svn-id: http://core.svn.wordpress.org/trunk@45450 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/rest-api/class-wp-rest-request.php

@@ -294,7 +294,9 @@ class WP_REST_Request implements ArrayAccess {
 	 *
 	 * @since 4.4.0
 	 *
-	 * @return array Map containing 'value' and 'parameters' keys.
+	 * @return array|null Map containing 'value' and 'parameters' keys
+	 *                    or null when no valid content-type header was
+	 *                    available.
 	 */
 	public function get_content_type() {
 		$value = $this->get_header( 'content-type' );
@@ -334,7 +336,7 @@ class WP_REST_Request implements ArrayAccess {
 		$order = array();
 
 		$content_type = $this->get_content_type();
-		if ( $content_type['value'] === 'application/json' ) {
+		if ( isset( $content_type['value'] ) && 'application/json' === $content_type['value'] ) {
 			$order[] = 'JSON';
 		}