Fix Absent::foldLeft bug (#121)

Co-authored-by: Alexander Bandukwala <[email protected]>
Co-authored-by: Skyler Lutz <[email protected]>

Author: 7h3kk1d

src/main/java/com/jnape/palatable/lambda/semigroup/builtin/Absent.java

@@ -72,7 +72,7 @@ public Maybe<A> checkedApply(Maybe<A> maybeX, Maybe<A> maybeY) {
             @Override
             public Maybe<A> foldLeft(Maybe<A> acc, Iterable<Maybe<A>> maybes) {
                 return trampoline(
-                        into((res, it) -> res.equals(nothing())
+                        into((res, it) -> res.equals(nothing()) || !it.hasNext()
                                 ? terminate(res)
                                 : recurse(tuple(liftA2(aSemigroup, res, it.next()), it))),
                         tuple(acc, maybes.iterator()));

src/test/java/com/jnape/palatable/lambda/semigroup/builtin/AbsentTest.java

@@ -71,6 +71,13 @@ public void foldLeftShortCircuit() {
         assertEquals(nothing(), result);
     }
 
+    @Test
+    public void foldLeftWorksForJusts() {
+        Maybe<Unit> result = Absent.<Unit>absent(Constantly::constantly)
+                .foldLeft(just(UNIT), Arrays.asList(just(UNIT), just(UNIT)));
+        assertEquals(just(UNIT), result);
+    }
+
     @Test(timeout = 200)
     public void checkedApplyFoldRightShortCircuit() {
         Maybe<Unit> result = Absent.<Unit>absent().checkedApply(Constantly::constantly)