fix: influxdbexporter init panics

Closes open-telemetry#27084

exporter/influxdbexporter/writer.go

@@ -88,15 +88,21 @@ func composeWriteURL(config *Config) (string, error) {
 		queryValues.Set("db", config.V1Compatibility.DB)
 
 		if config.V1Compatibility.Username != "" && config.V1Compatibility.Password != "" {
-			var basicAuth []byte
-			base64.StdEncoding.Encode(basicAuth, []byte(config.V1Compatibility.Username+":"+string(config.V1Compatibility.Password)))
-			config.HTTPClientSettings.Headers["Authorization"] = configopaque.String("Basic " + string(basicAuth))
+			basicAuth := base64.StdEncoding.EncodeToString(
+				[]byte(config.V1Compatibility.Username + ":" + string(config.V1Compatibility.Password)))
+			if config.HTTPClientSettings.Headers == nil {
+				config.HTTPClientSettings.Headers = make(map[string]configopaque.String, 1)
+			}
+			config.HTTPClientSettings.Headers["Authorization"] = configopaque.String("Basic " + basicAuth)
 		}
 	} else {
 		queryValues.Set("org", config.Org)
 		queryValues.Set("bucket", config.Bucket)
 
 		if config.Token != "" {
+			if config.HTTPClientSettings.Headers == nil {
+				config.HTTPClientSettings.Headers = make(map[string]configopaque.String, 1)
+			}
 			config.HTTPClientSettings.Headers["Authorization"] = "Token " + config.Token
 		}
 	}

exporter/influxdbexporter/writer_test.go

@@ -186,3 +186,24 @@ func Test_influxHTTPWriterBatch_EnqueuePoint_emptyTagValue(t *testing.T) {
 		assert.Equal(t, "m,k=v f=1i 1000000002000", strings.TrimSpace(string(recordedRequestBody)))
 	}
 }
+
+func Test_composeWriteURL_doesNotPanic(t *testing.T) {
+	assert.NotPanics(t, func() {
+		cfg := &Config{}
+		_, err := composeWriteURL(cfg)
+		assert.NoError(t, err)
+	})
+
+	assert.NotPanics(t, func() {
+		cfg := &Config{
+			V1Compatibility: V1Compatibility{
+				Enabled:  true,
+				DB:       "my-db",
+				Username: "my-username",
+				Password: "my-password",
+			},
+		}
+		_, err := composeWriteURL(cfg)
+		assert.NoError(t, err)
+	})
+}