[AFP-58] Work on DELETE product controller

src/main/java/com/nisum/ascend/inventory/exception/ResourceNotFoundException.java

+package com.nisum.ascend.inventory.exception;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.web.bind.annotation.ResponseStatus;
+
+@ResponseStatus(value = HttpStatus.NOT_FOUND)
+public class ResourceNotFoundException extends Exception{
+    HttpStatus status;
+
+    public ResourceNotFoundException(HttpStatus status, String message) {
+        super(message);
+        this.status = status;
+    }
+}

src/main/java/com/nisum/ascend/inventory/service/ProductService.java

 package com.nisum.ascend.inventory.service;
 
 import com.nisum.ascend.inventory.dto.ProductDto;
+import com.nisum.ascend.inventory.exception.ResourceNotFoundException;
 import com.nisum.ascend.inventory.model.Product;
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.http.HttpStatus;
 import org.springframework.stereotype.Service;
 import reactor.core.publisher.Flux;
 import com.nisum.ascend.inventory.repository.ProductRepository;
@@ -20,7 +22,8 @@ public class ProductService {
                 .findBySku(sku)
                 .map(ProductDto::generateDtoFromProduct)
                 .flatMap(existingProduct -> productRepository.deleteProduct(existingProduct)
-                        .then(Mono.just(existingProduct))); //Insert Exception Handling after AFP-56 merge
+                        .then(Mono.just(existingProduct)))
+                .switchIfEmpty(Mono.error(new ResourceNotFoundException(HttpStatus.NOT_FOUND, "product not found")));
     }
 
 }