#vulnerable code 
                                @Test
    public void testRenderingOfStringObjectPairsWorks() {  
        String object1 = new String("stringy1");
        String object2 = new String("stringy2");
        
        // step 1: add one object.
        Result result = new Result(200);
        result.render("object1", object1);
        result.render("object2", object2);
        Map<String, Object> resultMap = (Map) result.getRenderable();       
        
        assertEquals(object1, resultMap.get("object1"));
        assertEquals(object2, resultMap.get("object2"));
        
        
        ///////////////////////////////////////////////////////////////////////
        // check that empty render throws exception
        ///////////////////////////////////////////////////////////////////////
        boolean gotException = false;
        try {
            
            // will throw exception
            result.render();
            
        } catch (IllegalArgumentException e) {
            gotException = true;
        }
                
        assertTrue(gotException);
        
        ///////////////////////////////////////////////////////////////////////
        // check that too many arguments in render(...) throws exception
        ///////////////////////////////////////////////////////////////////////
        gotException = false;
        try {
            
            // will throw exception
            result.render(object1, object2, new String("three"));
            
        } catch (IllegalArgumentException e) {
            gotException = true;
        }
                
        assertTrue(gotException);
        
        
        ///////////////////////////////////////////////////////////////////////
        // check that "correct" two string render throws exception
        // when first parameter is not a string
        ///////////////////////////////////////////////////////////////////////
        gotException = false;
        try {
            
            // will throw exception
            result.render(new TestObject(), object2);
            
        } catch (IllegalArgumentException e) {
            gotException = true;
        }
                
        assertTrue(gotException);
      
    } 
                            #location 12 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Test
    public void testRenderingOfStringObjectPairsWorks() {  
        String object1 = new String("stringy1");
        String object2 = new String("stringy2");
        
        // step 1: add one object.
        Result result = new Result(200);
        result.render("object1", object1);
        result.render("object2", object2);
        Map<String, Object> resultMap = (Map) result.getRenderable();       
        
        assertEquals(object1, resultMap.get("object1"));
        assertEquals(object2, resultMap.get("object2"));       
      
    }