Merge pull request #8891 from IgniteUI/ibarakov/fix-8853-11.0.x

fix(excel-export): use field if header is undefined or empty

Author: kdinev

projects/igniteui-angular/src/lib/services/exporter-common/base-export-service.ts

@@ -128,7 +128,7 @@ export abstract class IgxBaseExporter {
         let lastVisbleColumnIndex = -1;
 
         columns.forEach((column) => {
-            const columnHeader = column.header !== '' ? column.header : column.field;
+            const columnHeader = !ExportUtilities.isNullOrWhitespaces(column.header) ? column.header : column.field;
             const exportColumn = !column.hidden || options.ignoreColumnsVisibility;
             const index = options.ignoreColumnsOrder ? column.index : column.visibleIndex;
             const columnWidth = Number(column.width.slice(0, -2));