[COLLECTIONS-737]: Return 0 immeditaly if the given iterable is null in IterableUtils#size. Update tests.

src/main/java/org/apache/commons/collections4/IterableUtils.java

@@ -797,6 +797,9 @@ public class IterableUtils {
      * @return the number of elements contained in the iterable
      */
     public static int size(final Iterable<?> iterable) {
+        if (iterable == null) {
+            return 0;
+        }
         if (iterable instanceof Collection<?>) {
             return ((Collection<?>) iterable).size();
         }

src/test/java/org/apache/commons/collections4/FluentIterableTest.java

@@ -416,12 +416,6 @@ public class FluentIterableTest {
 
     @Test
     public void size() {
-        try {
-            FluentIterable.of((Iterable<?>) null).size();
-            fail("expecting NullPointerException");
-        } catch (final NullPointerException npe) {
-            // expected
-        }
         assertEquals(0, FluentIterable.of(emptyIterable).size());
         assertEquals(IterableUtils.toList(iterableOdd).size(), FluentIterable.of(iterableOdd).size());
     }

src/test/java/org/apache/commons/collections4/IterableUtilsTest.java

@@ -579,4 +579,9 @@ public class IterableUtilsTest {
             // expected
         }
     }
+
+    @Test
+    public void size() {
+        assertEquals(0, IterableUtils.size(null));
+    }
 }