Added method to String.lua to check if a string is nil or empty.

diff --git a/String.lua b/String.lua
index a5374ca..477c154 100644
--- a/String.lua
+++ b/String.lua
@@ -144,3 +144,7 @@ function CES:Fit(s, l, d)
 	end
 	return parts
 end
+
+function CES:IsNullOrEmpty(s)
+	return s == nil or s == ""
+end