fix: do not send empty flare file to the agent (#7287)

Author: rochdev

packages/dd-trace/src/flare/index.js

@@ -64,7 +64,7 @@ const flare = {
   },
 
   _sendFile (task, file, filename) {
-    if (!file) return
+    if (!file || file.length === 0) return
 
     const form = new FormData()
 

packages/dd-trace/test/flare.spec.js

@@ -161,4 +161,22 @@ describe('Flare', () => {
 
     flare.send(task)
   })
+
+  it('should not send an empty file', done => {
+    const timer = setTimeout(() => done(), 100)
+
+    handler = req => {
+      const file = req.files[0]
+
+      if (file.originalname !== 'tracer_logs.txt') return
+
+      clearTimeout(timer)
+
+      done(new Error('Received empty file.'))
+    }
+
+    flare.enable(tracerConfig)
+    flare.prepare('debug')
+    flare.send(task)
+  })
 })