fix non-Java-8 compatible constructs in modules

Author: thjaeckle

policies/model/src/main/java/org/eclipse/ditto/policies/model/PolicyImporter.java

@@ -107,7 +107,7 @@ private static CompletionStage<Set<PolicyEntry>> mergeImportedPolicyEntries(
                         visited).toCompletableFuture())
                 .collect(Collectors.toList());
 
-        return CompletableFuture.allOf(importFutures.toArray(CompletableFuture[]::new))
+        return CompletableFuture.allOf(importFutures.toArray(new CompletableFuture[0]))
                 .thenApply(ignored -> {
                     final Set<PolicyEntry> result = new LinkedHashSet<>(baseEntries);
                     for (final CompletableFuture<Set<PolicyEntry>> future : importFutures) {

policies/model/src/main/java/org/eclipse/ditto/policies/model/signals/commands/query/RetrievePolicyImportTransitiveImportsResponse.java

@@ -180,7 +180,7 @@ public List<PolicyId> getTransitiveImports() {
         return transitiveImports.stream()
                 .map(JsonValue::asString)
                 .map(PolicyId::of)
-                .collect(Collectors.toUnmodifiableList());
+                .collect(Collectors.collectingAndThen(Collectors.toList(), Collections::unmodifiableList));
     }
 
     @Override