PolicyDocument in ram.GetPolicyResponse is empty

[LicaSterian]

I made a ram.GetPolicy request but the PolicyDocument field of the response returned empty.

PolicyName:AdministratorAccess
PolicyType:System
Description:管理所有阿里云资源的权限
DefaultVersion:v1
PolicyDocument: 
CreateDate:2015-04-28T16:15:44Z
UpdateDate:2017-04-27T16:48:07Z
AttachmentCount:1

After calling GetHttpContentString on the GetPolicyResponse instance i noticed that the PolicyDocument is present:

{ "Policy":{ "UpdateDate":"2017-04-27T16:48:07Z", "PolicyType":"System", "Description":"管理所有阿里云资源的权限", "AttachmentCount":1, "DefaultVersion":"v1", "PolicyName":"AdministratorAccess", "CreateDate":"2015-04-28T16:15:44Z" }, "RequestId":"9C41103A-150E-4062-A22E-F8E6F9AE9FB5", "DefaultPolicyVersion":{ "VersionId":"v1", "IsDefaultVersion":true, "PolicyDocument":"\n{\n \"Statement\": [\n {\n \"Action\": \"*\",\n \"Effect\": \"Allow\",\n \"Resource\": \"*\"\n }\n ],\n \"Version\": \"1\"\n}\n ", "CreateDate":"2015-04-28T16:15:44Z" } }

It's under the DefaultPolicyVersion key (DefaultPolicyVersion.PolicyDocument).