fix: resolves some errors with the mcp tool to export documents by query

Author: Sandro Lange

ExportPaperless.Excel/Services/ExcelExportService.cs

@@ -64,7 +64,7 @@ public MemoryStream GenerateExcel(List<PaperlessDocument> documents, List<string
             FormatCellAsHyperlink(doc.Url.ToString(), urlCell);
             row.Append(urlCell);
 
-            if (customFields == null)
+            if (customFields != null)
             {
                 foreach (var fieldName in customFields)
                 {

ExportPaperless.McpServer/Tools/ExportFromPaperlessTools.cs

@@ -72,9 +72,9 @@ public async Task<IEnumerable<AIContent>> ExportSavedViewMetadata(
     public async Task<IEnumerable<AIContent>> ExportPaperlessDocumentsByQuery(
         HttpClient httpClient,
         [Description("The from date filter specifying to list all documents created after or at the given date")]
-        DateTime? from,
+        DateTime from,
         [Description("The to date filter specifying to list all documents created before or at the given date")]
-        DateTime? to,
+        DateTime to,
         [Description("The tags to filter documents by, documents include all given tags")]
         List<string> includeTags,
         [Description("The tags to exclude documents by, documents must not have these given tags")]