Fix JSON deserialization error in LoadProductDataAsync when product data source is unavailable

src/cosmos-copilot.WebApp/Services/SemanticKernelService.cs

@@ -34,19 +34,19 @@
     /// <summary>
     /// System prompt to send with user prompts to instruct the model for chat session
     /// </summary>
     private readonly string _systemPrompt = @"
         You are an AI assistant that helps people find information.
         Provide concise answers that are polite and professional.";
 
     /// <summary>
     /// System prompt to send with user prompts as a Retail AI Assistant for chat session
     /// </summary>
     private readonly string _systemPromptRetailAssistant = @"";
 
     /// <summary>    
     /// System prompt to send with user prompts to instruct the model for summarization
     /// </summary>
     private readonly string _summarizePrompt = @"
         Summarize this text. One to three words maximum length. 
         Plain text only. No punctuation, markup or tags.";
 
@@ -252,12 +252,49 @@
             string json = "";
             string jsonFilePath = _productDataSourceURI;
             HttpClient client = new HttpClient();
-            HttpResponseMessage response = await client.GetAsync(jsonFilePath);
-            if(response.IsSuccessStatusCode)
+
+            try
+            {
+                HttpResponseMessage response = await client.GetAsync(jsonFilePath);
+                if(response.IsSuccessStatusCode)
+                {
+                    json = await response.Content.ReadAsStringAsync();
+                }
+                else
+                {
+                    Console.WriteLine($"Failed to fetch product data from {jsonFilePath}. Status code: {response.StatusCode}");
+                    return;
+                }
+            }
+            catch (Exception ex)
+            {
+                Console.WriteLine($"Error fetching product data from {jsonFilePath}: {ex.Message}");
+                return;
+            }
+
+            // Validate that we have JSON content before attempting to deserialize
+            if (string.IsNullOrWhiteSpace(json))
+            {
+                Console.WriteLine($"Product data source returned empty content from {jsonFilePath}");
+                return;
+            }
+
+            List<Product>? products = null;
+            try
+            {
+                products = JsonSerializer.Deserialize<List<Product>>(json);
+            }
+            catch (JsonException ex)
+            {
+                Console.WriteLine($"Error deserializing product data: {ex.Message}");
+                return;
+            }
+
+            if (products == null || products.Count == 0)
             {
-                json = await response.Content.ReadAsStringAsync();
+                Console.WriteLine("No products found in the data source");
+                return;
             }
-            List<Product> products = JsonSerializer.Deserialize<List<Product>>(json)!;
 
             foreach (var product in products)
             {