get returns Memcached::NotFound exception after set expire

lib/memcached.rb

@@ -1,5 +1,6 @@
 require 'java'
 require 'memcached/version'
+require 'memcached/exceptions'
 require 'target/spymemcached-ext-0.0.1.jar'
 
 class Memcached
@@ -41,6 +42,9 @@ def set(key, value, ttl=@default_ttl, marshal=true, flags=FLAGS)
 
   def get(key, marshal=true)
     ret = @client.get(key, @simple_transcoder)
+    if ret.nil?
+      raise Memcached::NotFound
+    end
     flags, data = ret.flags, ret.data
     value = String.from_java_bytes data
     marshal ? Marshal.load(value) : value

lib/memcached/exceptions.rb

@@ -0,0 +1 @@
+class Memcached::NotFound < Exception; end

spec/memcached_spec.rb

@@ -22,13 +22,20 @@
     end
 
     it "should set/get with plain text" do
-      @memcached.set("hello", "world")
-      @memcached.get("hello").should == "world"
+      @memcached.set "key", "value"
+      @memcached.get("key").should == "value"
     end
 
     it "should set/get with compressed text" do
-      @memcached.set("hello", "x\234c?P?*?/?I\001\000\b8\002a")
-      @memcached.get("hello").should == "x\234c?P?*?/?I\001\000\b8\002a"
+      @memcached.set "key", "x\234c?P?*?/?I\001\000\b8\002a"
+      @memcached.get("key").should == "x\234c?P?*?/?I\001\000\b8\002a"
+    end
+
+    it "should set expiry" do
+      @memcached.set "key", "value", 1
+      @memcached.get("key").should == "value"
+      sleep 1
+      lambda { @memcached.get("key") }.should raise_error(Memcached::NotFound)
     end
   end
 end