fix(exporters): added callback for when data is empty #6673

Author: igdmdimitrov

projects/igniteui-angular/src/lib/services/csv/char-separated-value-data.ts

@@ -39,13 +39,13 @@ export class CharSeparatedValueData {
 
     public prepareDataAsync(done: (result: string) => void) {
         if (!this._data || this._data.length === 0) {
-            return '';
+            done('');
         }
 
         const keys = ExportUtilities.getKeysFromData(this._data);
 
         if (keys.length === 0) {
-            return '';
+            done('');
         }
 
         this._isSpecialData = ExportUtilities.isSpecialData(this._data);

projects/igniteui-angular/src/lib/services/excel/excel-files.ts

@@ -145,14 +145,15 @@ export class WorksheetFile implements IExcelFile {
         });
     }
 
-    private prepareDataAsync(worksheetData: WorksheetData, done: (cols: string, rows: string) => void) {
+    private prepareDataAsync(worksheetData: WorksheetData, done: (cols: string, sheetData: string) => void) {
         let sheetData = '';
         let cols = '';
         const dictionary = worksheetData.dataDictionary;
 
         if (worksheetData.isEmpty) {
             sheetData += '<sheetData/>';
             this.dimension = 'A1';
+            done('', sheetData);
         } else {
             sheetData += '<sheetData>';
             const height =  worksheetData.options.rowHeight;