Ensure $? is not nil

Author: fukayatsu

Diff for: Ruby/lib/terminal-notifier.rb

@@ -50,7 +50,7 @@ def self.execute(verbose, options)
   # Raises if not supported on the current platform.
   def notify(message, options = {}, verbose = false)
     TerminalNotifier.execute(verbose, options.merge(:message => message))
-    $?.success?
+    $? && $?.success?
   end
   module_function :notify
 
@@ -60,7 +60,7 @@ def notify(message, options = {}, verbose = false)
   # If no ‘group’ ID is given, all notifications are removed.
   def remove(group = 'ALL', verbose = false)
     TerminalNotifier.execute(verbose, :remove => group)
-    $?.success?
+    $? && $?.success?
   end
   module_function :remove