Work towards #56: Splitting up the README

I did the job and splitted up the readme, hopefully everything was
splitted correctly...

null-object/index.md

@@ -0,0 +1,22 @@
+---
+layout: pattern
+title: Null Object
+folder: null-object
+categories: pattern_cat
+tags: pattern_tag
+---
+
+**Intent:** In most object-oriented languages, such as Java or C#, references
+may be null. These references need to be checked to ensure they are not null
+before invoking any methods, because methods typically cannot be invoked on
+null references. Instead of using a null reference to convey absence of an
+object (for instance, a non-existent customer), one uses an object which
+implements the expected interface, but whose method body is empty. The
+advantage of this approach over a working default implementation is that a Null
+Object is very predictable and has no side effects: it does nothing.
+
+![alt text](./etc/null-object.png "Null Object")
+
+**Applicability:** Use the Null Object pattern when
+
+* you want to avoid explicit null checks and keep the algorithm elegant and easy to read.