avoiding isEmpty() of optional, as not present in java 8

Author: Kajetan Fuchsberger

src/java/org/tensorics/core/tensorbacked/ProxiedInterfaceTensorbackeds.java

@@ -101,7 +101,7 @@ public boolean equals(Object obj) {
                 return false;
             }
             Optional<DelegatingInvocationHandler<?, ?>> otherIh = invokationHandlerFrom((Tensorbacked) obj);
-            if (otherIh.isEmpty()) {
+            if (!otherIh.isPresent()) {
                 return false;
             }
             DelegatingInvocationHandler<?, ?> other = otherIh.get();