[Eng]: version bump will be failed if repo contains new module

[dingmeng-xue]

Description

When we introduce new module, it doesn't have serialized cmdlets information under Tools.Common folder. It leads version bump is failed.

Unhandled exception. System.ArgumentNullException: Value cannot be null. (Parameter 'path')
   at System.IO.File.WriteAllText(String path, String contents)
   at VersionController.Models.VersionMetadataHelper.SerializeCmdlets(String fileName, ModuleMetadata moduleMetadata) in C:\Dev\Azure\azure-powershell\tools\VersionController\Models\VersionMetadataHelper.cs:line 70
   at VersionController.Models.VersionBumper.UpdateSerializedCmdlet() in C:\Dev\Azure\azure-powershell\tools\VersionController\Models\VersionBumper.cs:line 337
   at VersionController.Models.VersionBumper.BumpAllVersions() in C:\Dev\Azure\azure-powershell\tools\VersionController\Models\VersionBumper.cs:line 73
   at VersionController.Program.BumpVersions() in C:\Dev\Azure\azure-powershell\tools\VersionController\Program.cs:line 214
   at VersionController.Program.Main(String[] args) in C:\Dev\Azure\azure-powershell\tools\VersionController\Program.cs:line 78

The stack trace points to below method

azure-powershell/tools/VersionController/Models/VersionMetadataHelper.cs

Line 61 in 0c7e72d

public static void SerializeCmdlets(string fileName, ModuleMetadata moduleMetadata)