Fix error telemetry issue

Fixes #102558

src/vs/workbench/contrib/terminal/browser/links/terminalLinkHelpers.ts

@@ -94,13 +94,16 @@ export function convertBufferRangeToViewport(bufferRange: IBufferRange, viewport
 }
 
 export function getXtermLineContent(buffer: IBuffer, lineStart: number, lineEnd: number, cols: number): string {
-	let line = '';
+	let content = '';
 	for (let i = lineStart; i <= lineEnd; i++) {
 		// Make sure only 0 to cols are considered as resizing when windows mode is enabled will
 		// retain buffer data outside of the terminal width as reflow is disabled.
-		line += buffer.getLine(i)!.translateToString(true, 0, cols);
+		const line = buffer.getLine(i);
+		if (line) {
+			content += line.translateToString(true, 0, cols);
 		}
-	return line;
+	}
+	return content;
 }
 
 export function positionIsInRange(position: IBufferCellPosition, range: IBufferRange): boolean {