updated push(), updated size()

src/main/java/MyStack.java

 public class MyStack {
+
+    private Object element;
+
     public MyStack() {
         super();
+        element = null;
     }
 
     public int size() {
-        return 0;
+        return (element == null) ? 0 : 1;
     }
 
     public void push(Object element) {
-        ;
+        this.element = element;
     }
 }