refactor: 增加空检查

Author: ArgoZhang

src/BootstrapBlazor/Components/Button/PopConfirmButton.razor.cs

@@ -99,7 +99,11 @@ private async Task OnClickConfirm()
             IsDisabled = true;
             IsAsyncLoading = true;
             StateHasChanged();
-            await OnConfirm();
+
+            if (OnConfirm != null)
+            {
+                await OnConfirm();
+            }
 
             if (ButtonType == ButtonType.Submit)
             {