chore: do not flush empty batch span processor

Author: dyladan

packages/opentelemetry-tracing/src/export/BatchSpanProcessor.ts

@@ -45,7 +45,7 @@ export class BatchSpanProcessor implements SpanProcessor {
         : DEFAULT_BUFFER_TIMEOUT_MS;
 
     this._timer = setInterval(() => {
-      if (Date.now() - this._lastSpanFlush >= this._bufferTimeout) {
+      if (this._shouldFlush()) {
         this._flush();
       }
     }, this._bufferTimeout);
@@ -73,6 +73,13 @@ export class BatchSpanProcessor implements SpanProcessor {
     }
   }
 
+  private _shouldFlush(): boolean {
+    return (
+      this._finishedSpans.length >= 0 &&
+      Date.now() - this._lastSpanFlush >= this._bufferTimeout
+    );
+  }
+
   /** Send the span data list to exporter */
   private _flush() {
     this._exporter.export(this._finishedSpans, () => {});