Add case for when user agent is nil

Add test for nil user agent

rootfs/etc/nginx/lua/test/util/same_site_test.lua

@@ -1,4 +1,8 @@
 describe("same_site_compatible_test", function()
+  it("returns true for nil user agent", function()
+    local same_site = require("util.same_site")
+    assert.True(same_site.same_site_none_compatible(nil))
+  end)
   it("returns false for chrome 4", function()
     local same_site = require("util.same_site")
     assert.False(same_site.same_site_none_compatible("Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2704.103 Safari/537.36"))

rootfs/etc/nginx/lua/util/same_site.lua

@@ -13,7 +13,9 @@ local _M = {}
 -- browsers which will reject SameSite=None cookies.
 -- reference: https://www.chromium.org/updates/same-site/incompatible-clients
 function _M.same_site_none_compatible(user_agent)
-  if string.match(user_agent, "Chrome/4") then
+  if not user_agent then
+    return true
+  elseif string.match(user_agent, "Chrome/4") then
     return false
   elseif string.match(user_agent, "Chrome/5") then
     return false