Fixes 4529: Updated IPart to match new ICapabilityProvider (#4534)

src/main/java/appeng/fluids/helper/DualityFluidInterface.java

@@ -210,7 +210,7 @@ public class DualityFluidInterface
         } else if (capabilityClass == Capabilities.STORAGE_MONITORABLE_ACCESSOR) {
             return (LazyOptional<T>) LazyOptional.of(() -> this.accessor);
         }
-        return null;
+        return LazyOptional.empty();
     }
 
     private boolean hasConfig() {

src/main/java/appeng/tile/networking/CableBusTileEntity.java

@@ -311,7 +311,7 @@ public class CableBusTileEntity extends AEBaseTileEntity implements AEMultiTile
         IPart part = this.getPart(partLocation);
         LazyOptional<T> result = part == null ? LazyOptional.empty() : part.getCapability(capabilityClass);
 
-        if (result != null) {
+        if (result.isPresent()) {
             return result;
         }