fixes #90974

src/vs/workbench/contrib/debug/browser/repl.ts

@@ -149,10 +149,12 @@ export class Repl extends ViewPane implements IHistoryNavigationWidget {
 										if (item && item.label) {
 											let insertTextRules: CompletionItemInsertTextRule | undefined = undefined;
 											let insertText = item.text || item.label;
-											if (typeof item.selectionStart === 'number' && typeof item.selectionLength === 'number') {
+											if (typeof item.selectionStart === 'number') {
 												// If a debug completion item sets a selection we need to use snippets to make sure the selection is selected #90974
 												insertTextRules = CompletionItemInsertTextRule.InsertAsSnippet;
-												insertText = insertText.substr(0, item.selectionStart) + '${1:' + insertText.substr(item.selectionStart, item.selectionLength) + '}$0' + insertText.substr(item.selectionStart + item.selectionLength);
+												const selectionLength = typeof item.selectionLength === 'number' ? item.selectionLength : 0;
+												const placeholder = selectionLength > 0 ? '${1:' + insertText.substr(item.selectionStart, selectionLength) + '}$0' : '$0';
+												insertText = insertText.substr(0, item.selectionStart) + placeholder + insertText.substr(item.selectionStart + selectionLength);
 											}
 
 											suggestions.push({