code: public void putContext(Class key, Object contextObject) {
          if((key == null) || (contextObject == null)) {
              throw new NullPointerException();
          }
          map.put(key, contextObject);
      }
docs: Associates a context object with this <code>ELContext</code>.
  
  <p>The <code>ELContext</code> maintains a collection of context objects
  relevant to the evaluation of an expression. These context objects
  are used by <code>ELResolver</code>s.  This method is used to
  add a context object to that collection.</p>
  
  <p>By convention, the <code>contextObject</code> will be of the
  type specified by the <code>key</code>.  However, this is not
  required and the key is used strictly as a unique identifier.</p>
  
  @param key The key used by an @{link ELResolver} to identify this
  context object.
  @param contextObject The context object to add to the collection.
  @throws NullPointerException if key is null or contextObject is null.