fix #435

Author: abuzuhri

Source/FikaAmazonAPI/AmazonConnection.cs

@@ -1,4 +1,5 @@
-using FikaAmazonAPI.Services;
+using FikaAmazonAPI.AmazonSpApiSDK.Models.Exceptions;
+using FikaAmazonAPI.Services;
 using FikaAmazonAPI.Utils;
 using System;
 
@@ -99,6 +100,8 @@ private void Authenticate(AmazonCredential Credentials)
 
         private void Init(AmazonCredential Credentials)
         {
+            ValidateCredentials(Credentials);
+
             this.Credentials = Credentials;
 
             this._Authorization = new AuthorizationService(this.Credentials);
@@ -137,7 +140,25 @@ private void Init(AmazonCredential Credentials)
             this._VendorDirectFulfillmentOrders = new VendorDirectFulfillmentOrderService(this.Credentials);
             this._VendorOrders = new VendorOrderService(this.Credentials);
         }
-
+        private void ValidateCredentials(AmazonCredential Credentials)
+        {
+            if (Credentials == null)
+                throw new AmazonUnauthorizedException($"Error, you cannot make calls to Amazon without credentials!");
+            else if (string.IsNullOrEmpty(Credentials.AccessKey))
+                throw new AmazonInvalidInputException($"InvalidInput, AccessKey cannot be empty!");
+            else if (string.IsNullOrEmpty(Credentials.SecretKey))
+                throw new AmazonInvalidInputException($"InvalidInput, SecretKey  cannot be empty!");
+            else if (string.IsNullOrEmpty(Credentials.RoleArn))
+                throw new AmazonInvalidInputException($"InvalidInput, RoleArn cannot be empty!");
+            else if (string.IsNullOrEmpty(Credentials.ClientId))
+                throw new AmazonInvalidInputException($"InvalidInput, ClientId cannot be empty!");
+            else if (string.IsNullOrEmpty(Credentials.ClientSecret))
+                throw new AmazonInvalidInputException($"InvalidInput, ClientSecret  cannot be empty!");
+            else if (string.IsNullOrEmpty(Credentials.RefreshToken))
+                throw new AmazonInvalidInputException($"InvalidInput, RefreshToken cannot be empty!");
+            else if (Credentials.MarketPlace == null)
+                throw new AmazonInvalidInputException($"InvalidInput, MarketPlace cannot be null!");
+        }
         public MarketPlace GetCurrentMarketplace { get { return Credentials.MarketPlace; } }
     }
 }