Don't use an anonymous function to trigger admin notices

stream.php

@@ -77,6 +77,9 @@ private function __construct() {
 		// Install the plugin
 		add_action( 'wp_stream_before_db_notices', array( __CLASS__, 'install' ) );
 
+		// Trigger admin notices
+		add_action( 'all_admin_notices', array( __CLASS__, 'admin_notices' ) );
+
 		// Load languages
 		add_action( 'plugins_loaded', array( __CLASS__, 'i18n' ) );
 
@@ -248,7 +251,7 @@ public static function is_valid_php_version() {
 	}
 
 	/**
-	 * Show an error or other message, using admin_notice or WP-CLI logger
+	 * Handle notice messages according to the appropriate context (WP-CLI or the WP Admin)
 	 *
 	 * @param string $message
 	 * @param bool $is_error
@@ -263,15 +266,28 @@ public static function notice( $message, $is_error = true ) {
 				WP_CLI::success( $message );
 			}
 		} else {
-			$print_message = function () use ( $message, $is_error ) {
-				$class_name   = ( $is_error ? 'error' : 'updated' );
-				$html_message = sprintf( '<div class="%s">%s</div>', $class_name, wpautop( $message ) );
-				echo wp_kses_post( $html_message );
-			};
-			add_action( 'all_admin_notices', $print_message );
+			self::admin_notices( $message, $is_error );
 		}
 	}
 
+	/**
+	 * Show an error or other message in the WP Admin
+	 *
+	 * @param string $message
+	 * @param bool $is_error
+	 * @return void
+	 */
+	public static function admin_notices( $message, $is_error = true ) {
+		if ( empty( $message ) ) {
+			return;
+		}
+
+		$class_name   = $is_error ? 'error' : 'updated';
+		$html_message = sprintf( '<div class="%s">%s</div>', esc_attr( $class_name ), wpautop( $message ) );
+
+		echo wp_kses_post( $html_message );
+	}
+
 	/**
 	 * Displays an HTML comment in the frontend head to indicate that Stream is activated,
 	 * and which version of Stream is currently in use.