fix(rum-core): fix for merge utility function (#1555)

Author: david-luna

package-lock.json

@@ -190,7 +190,7 @@ class Config {
         Math.round(transactionSampleRate * 10000) / 10000
     }
 
-    merge(this.config, properties)
+    this.config = merge(this.config, properties)
     this.events.send(CONFIG_CHANGE, [this.config])
   }
 

packages/rum-core/src/common/config-service.js

@@ -284,12 +284,12 @@ function getCurrentScript() {
   }
 }
 
-function extend(dst) {
-  return baseExtend(dst, slice.call(arguments, 1), false)
+function extend() {
+  return baseExtend(Object.create(null), slice.call(arguments), false)
 }
 
-function merge(dst) {
-  return baseExtend(dst, slice.call(arguments, 1), true)
+function merge() {
+  return baseExtend(Object.create(null), slice.call(arguments), true)
 }
 
 function isUndefined(obj) {

packages/rum-core/src/common/utils.js

@@ -77,7 +77,7 @@ class SpanBase {
   addContext(...context) {
     if (context.length === 0) return
     this.ensureContext()
-    merge(this.context, ...context)
+    this.context = merge(this.context, ...context)
   }
 
   end(endTime) {

packages/rum-core/src/performance-monitoring/span-base.js

@@ -88,7 +88,7 @@ class Transaction extends SpanBase {
       // is not setting explicitly the threshold and instead expecting to rely on the one by default.
       this.options.reuseThreshold = options.reuseThreshold
 
-      extend(this.options, options)
+      this.options = extend(this.options, options)
     }
   }