fixed error when domain is nil

lib/simpleidn.rb

@@ -223,6 +223,7 @@ def encode(input)
   #   SimpleIDN.to_ascii("møllerriis.com")
   #    => "xn--mllerriis-l8a.com" 
   def to_ascii(domain) 
+    return if domain.nil?
     domain_array = domain.split(".")
     out = []
     i = 0
@@ -239,6 +240,7 @@ def to_ascii(domain)
   #   SimpleIDN.to_unicode("xn--mllerriis-l8a.com")
   #    => "møllerriis.com" 
   def to_unicode(domain)
+    return if domain.nil?
     domain_array = domain.split(".")
     out = []
     i = 0

spec/idn.rb

@@ -14,7 +14,13 @@
     it "should respect * and not try to decode it" do
       SimpleIDN.to_unicode("*.xn--mllerriis-l8a.com").should == "*.møllerriis.com"
     end
+
+    it "should return nil for nil" do
+      SimpleIDN.to_unicode(nil).should be_nil
+    end
+
   end
+
   describe "to_ascii" do
     it "should pass all test cases" do
       TESTCASES_JOSEFSSON.sort.each do |testcase, vector|
@@ -25,5 +31,10 @@
     it "should respect * and not try to encode it" do
 			SimpleIDN.to_ascii("*.hello.com").should == "*.hello.com"
 		end
+
+
+    it "should return nil for nil" do
+      SimpleIDN.to_ascii(nil).should be_nil
+    end
   end
 end