feat: Make log.meta optional (#16)

* Add check if msg and meta properties are deleted

* Add fast check before deleting the property

* Give log.meta priority in meta object and adjust tests

* Add unit test for Should delete the msg and meta property

* Make log.meta optional

* Remove unnecessary Object.assign statement

* Apply meta type check

* Add unit tests covering empty strings

Author: kruczyna

lib/cloud-logging.js

@@ -80,10 +80,9 @@ class CloudLogging {
       return
     }
 
-    const meta = Object.assign(
-      log.meta, // Custom property to add more meta to the LogEntry
-      { severity: this.mapSeverity(log.level) }
-    )
+    const meta = typeof (log.meta) === 'object'
+      ? Object.assign(log.meta, { severity: this.mapSeverity(log.level) })
+      : { severity: this.mapSeverity(log.level) }
 
     if (log.meta) {
       delete log.meta