Fix for missing upgradeGuid parsed as empty string
Fix for missing upgradeGuid parsed as empty string

hglkrijger/WALinuxAgent,rjschwei/WALinuxAgent,andyliuliming/WALinuxAgent,hglkrijger/WALinuxAgent,andyliuliming/WALinuxAgent,Azure/WALinuxAgent,rjschwei/WALinuxAgent,Azure/WALinuxAgent