Minor refactorings and code style changes (#807)

* Made minor changes in some patterns such as removed throws clause where not needed, changed incorrect order of arguments in assertEquals

* Minor refactorings and code style changes. 1) Removed several use of raw types 2) Removed unnecessary throws clauses 3) Used lambda expressions wherever applicable 4) Used apt assertion methods for readability 5) Use of try with resources wherever applicable 6) Corrected incorrect order of assertXXX arguments

* Removed unused import from Promise

* Addressed review comments

* Addressed checkstyle issue

null-object/src/test/java/com/iluwatar/nullobject/TreeTest.java

@@ -110,7 +110,7 @@ public class TreeTest {
   }
 
   @Test
-  public void testGetLeft() throws Exception {
+  public void testGetLeft() {
     final Node level1 = TREE_ROOT.getLeft();
     assertNotNull(level1);
     assertEquals("level1_a", level1.getName());
@@ -130,7 +130,7 @@ public class TreeTest {
   }
 
   @Test
-  public void testGetRight() throws Exception {
+  public void testGetRight() {
     final Node level1 = TREE_ROOT.getRight();
     assertNotNull(level1);
     assertEquals("level1_b", level1.getName());