diff --git a/sys/apis/ui.lua b/sys/apis/ui.lua
index f7363c0..f444c00 100644
--- a/sys/apis/ui.lua
+++ b/sys/apis/ui.lua
@@ -1219,7 +1219,7 @@ function UI.Page:focusNext()
 end
 
 function UI.Page:setFocus(child)
-	if not child.focus then
+	if not child or not child.focus then
 		return
 	end
 
diff --git a/sys/apis/util.lua b/sys/apis/util.lua
index 33344fa..eb50f58 100644
--- a/sys/apis/util.lua
+++ b/sys/apis/util.lua
@@ -489,6 +489,7 @@ function Util.insertString(str, istr, pos)
 end
 
 function Util.split(str, pattern)
+	if not str then error('Util:split: invalid parameters', 2) end
 	pattern = pattern or "(.-)\n"
 	local t = {}
 	local function helper(line) table.insert(t, line) return "" end