Little optmization

src/DallENet/DallEClient.cs

@@ -68,16 +68,15 @@ public async Task<DallEImageGenerationResponse> GenerateImagesAsync(string promp
                 await Task.Delay(retryAfter, cancellationToken);
 
                 response = await httpClient.GetFromJsonAsync<DallEImageGenerationResponse>(operationLocation, cancellationToken);
-                EnsureErrorIsSet(response!, httpResponse);
-                response!.OperationId = operationId ?? string.Empty;
+                NormalizeRenspose(response!, httpResponse, operationId);
 
-                isRunning = response.Status is "notRunning" or "running";
+                isRunning = response!.Status is "notRunning" or "running";
             }
         }
         else
         {
             response = await httpResponse.Content.ReadFromJsonAsync<DallEImageGenerationResponse>(cancellationToken: cancellationToken);
-            EnsureErrorIsSet(response!, httpResponse);
+            NormalizeRenspose(response!, httpResponse, null);
         }
 
         if (!response!.IsSuccessful && options.ThrowExceptionOnError)
@@ -96,7 +95,7 @@ public async Task DeleteImagesAsync(string operationId, CancellationToken cancel
         if (!httpResponse.IsSuccessStatusCode)
         {
             var response = await httpResponse.Content.ReadFromJsonAsync<DallEImageGenerationResponse>(cancellationToken: cancellationToken);
-            EnsureErrorIsSet(response!, httpResponse);
+            NormalizeRenspose(response!, httpResponse, operationId);
 
             throw new DallEException(response!.Error, httpResponse.StatusCode);
         }
@@ -110,8 +109,10 @@ private DallEImageGenerationRequest CreateRequest(string prompt, int? imageCount
             ImageCount = imageCount ?? options.DefaultImageCount
         };
 
-    private static void EnsureErrorIsSet(DallEImageGenerationResponse response, HttpResponseMessage httpResponse)
+    private static void NormalizeRenspose(DallEImageGenerationResponse response, HttpResponseMessage httpResponse, string? operationId)
     {
+        response.OperationId = operationId;
+
         if (!httpResponse.IsSuccessStatusCode && response.Error is null)
         {
             response.Error = new DallEError

src/DallENet/Models/Converters/UnixToDateTimeConverter.cs

@@ -18,7 +18,7 @@ public override DateTime Read(ref Utf8JsonReader reader, Type typeToConvert, Jso
                 var span = reader.HasValueSequence ? reader.ValueSequence.ToArray() : reader.ValueSpan;
                 if (Utf8Parser.TryParse(span, out long number, out var bytesConsumed) && span.Length == bytesConsumed)
                 {
-                    var date = UnixTimeStampToDateTime(number);
+                    var date = DateTimeOffset.FromUnixTimeSeconds(number).UtcDateTime;
                     return date;
                 }
             }
@@ -36,15 +36,6 @@ public override DateTime Read(ref Utf8JsonReader reader, Type typeToConvert, Jso
         }
 
         return DateTime.MinValue;
-
-        static DateTime UnixTimeStampToDateTime(double unixTimeStamp)
-        {
-            // Unix timestamp is seconds past epoch
-            var dateTime = new DateTime(1970, 1, 1, 0, 0, 0, 0, DateTimeKind.Utc);
-            dateTime = dateTime.AddSeconds(unixTimeStamp).ToUniversalTime();
-
-            return dateTime;
-        }
     }
 
     public override void Write(Utf8JsonWriter writer, DateTime value, JsonSerializerOptions options)

src/DallENet/Models/DallEImageGenerationResponse.cs

@@ -33,7 +33,7 @@ public class DallEImageGenerationResponse
     /// <summary>
     /// Gets or sets the Operation Id that identifies the original image generation request.
     /// </summary>
-    public string OperationId { get; set; } = string.Empty;
+    public string? OperationId { get; set; }
 
     /// <summary>
     /// Gets or sets the status of the response.