fix checkerframework regressions

Author: wadoon

key.util/src/main/java/org/key_project/util/collection/ImmutableArray.java

@@ -159,10 +159,10 @@ public String toString() {
 
     @Override
     public Iterator<S> iterator() {
-        return new ArrayIterator<>(this);
+        return new ArrayIterator<S>(this);
     }
 
-    private static class ArrayIterator<T> implements Iterator<T> {
+    private static class ArrayIterator<T extends @Nullable Object> implements Iterator<T> {
 
         private int i = 0;
         private final ImmutableArray<T> coll;

key.util/src/main/java/org/key_project/util/collection/Immutables.java

@@ -163,7 +163,7 @@ private Immutables() {
      *
      * @return the view onto the iterable as an immutable list
      */
-    public static <T> ImmutableList<T> createListFrom(Iterable<? extends T> iterable) {
+    public static <T extends @Nullable Object> ImmutableList<T> createListFrom(Iterable<? extends T> iterable) {
         ImmutableList<T> result = ImmutableSLList.nil();
         for (T t : iterable) {
             result = result.prepend(t);

key.util/src/test/java/org/key_project/util/collection/TestImmutables.java

@@ -148,20 +148,20 @@ public void testEqualityEmpty() {
 
     @Test
     public void testIntersectEmpty() {
-        ImmutableSet<Object> s0 = DefaultImmutableSet.nil();
-        ImmutableSet<Object> s1 = DefaultImmutableSet.nil().add("1");
-        ImmutableSet<Object> s2 = DefaultImmutableSet.nil().add("2");
+        var s0 = DefaultImmutableSet.nil();
+        var s1 = DefaultImmutableSet.nil().add("1");
+        var s2 = DefaultImmutableSet.nil().add("2");
 
-        ImmutableSet<Object> sIntersect = s1.intersect(s2);
+        var sIntersect = s1.intersect(s2);
         assertEquals(0, sIntersect.size());
         assertEquals(s0, sIntersect);
     }
 
     @Test
     public void testHashCodes() {
 
-        ImmutableSet<Object> s1 = DefaultImmutableSet.nil().add("one").add("two");
-        ImmutableSet<Object> s2 = DefaultImmutableSet.nil().add("two").add("one");
+        var s1 = DefaultImmutableSet.nil().add("one").add("two");
+        var s2 = DefaultImmutableSet.nil().add("two").add("one");
 
         assertEquals(s1, s2);
         int hash1 = s1.hashCode();