Make user_agent optional everywhere end also handle an explicit nil in ContentSecurityPolicy

Author: ptoomey3

lib/secure_headers/headers/content_security_policy.rb

@@ -13,6 +13,7 @@ class ContentSecurityPolicy
     FALLBACK_VERSION = ::UserAgent::Version.new("0")
 
     def initialize(config = nil, user_agent = OTHER)
+      user_agent ||= OTHER
       @config = if config.is_a?(Hash)
         if config[:report_only]
           ContentSecurityPolicyReportOnlyConfig.new(config || DEFAULT_CONFIG)

lib/secure_headers/headers/policy_management.rb

@@ -200,7 +200,7 @@ module ClassMethods
       #
       # Returns a default policy if no configuration is provided, or a
       # header name and value based on the config.
-      def make_header(config, user_agent)
+      def make_header(config, user_agent = nil)
         return if config.nil? || config == OPT_OUT
         header = new(config, user_agent)
         [header.name, header.value]