Fix inconsistent @throws comments in ListOrderedSet (#125)

* Fix inconsistent @throws comments in ListOrderedSet

* Fix inconsistent @throws comments in MultiKey and update the test cases for them.

src/main/java/org/apache/commons/collections4/keyvalue/MultiKey.java

@@ -126,7 +126,7 @@ public class MultiKey<K> implements Serializable {
      * This is equivalent to <code>new MultiKey(keys, true)</code>.
      *
      * @param keys  the array of keys, not null
-     * @throws IllegalArgumentException if the key array is null
+     * @throws NullPointerException if the key array is null
      */
     public MultiKey(final K[] keys) {
         this(keys, true);
@@ -153,13 +153,13 @@ public class MultiKey<K> implements Serializable {
      *
      * @param keys  the array of keys, not null
      * @param makeClone  true to clone the array, false to assign it
-     * @throws IllegalArgumentException if the key array is null
+     * @throws NullPointerException if the key array is null
      * @since 3.1
      */
     public MultiKey(final K[] keys, final boolean makeClone) {
         super();
         if (keys == null) {
-            throw new IllegalArgumentException("The array of keys must not be null");
+            throw new NullPointerException("The array of keys must not be null");
         }
         if (makeClone) {
             this.keys = keys.clone();

src/main/java/org/apache/commons/collections4/set/ListOrderedSet.java

@@ -147,7 +147,7 @@ public class ListOrderedSet<E>
      * Constructor that wraps (not copies).
      *
      * @param set the set to decorate, must not be null
-     * @throws IllegalArgumentException if set is null
+     * @throws NullPointerException if set is null
      */
     protected ListOrderedSet(final Set<E> set) {
         super(set);

src/test/java/org/apache/commons/collections4/keyvalue/MultiKeyTest.java

@@ -96,15 +96,15 @@ public class MultiKeyTest {
         try {
             new MultiKey<>(keys);
             fail();
-        } catch (final IllegalArgumentException ex) {}
+        } catch (final NullPointerException ex) {}
         try {
             new MultiKey<>(keys, true);
             fail();
-        } catch (final IllegalArgumentException ex) {}
+        } catch (final NullPointerException ex) {}
         try {
             new MultiKey<>(keys, false);
             fail();
-        } catch (final IllegalArgumentException ex) {}
+        } catch (final NullPointerException ex) {}
     }
 
     @Test