Initial data commit

Task/Null-object/Ruby/null-object.rb

@@ -0,0 +1,10 @@
+puts "@object is nil" if @object.nil?		# instance variable
+
+puts "$object is nil" if $object.nil?		# global variable, too
+
+# It recognizes as the local variable even if it isn't executed.
+object = 1  if false
+puts "object is nil" if object.nil?
+
+# nil itself is an object:
+puts nil.class  # => NilClass