code: public Observable<PolicyDefinitionInner> getAtManagementGroupAsync(String policyDefinitionName, String managementGroupId) {
          return getAtManagementGroupWithServiceResponseAsync(policyDefinitionName, managementGroupId).map(new Func1<ServiceResponse<PolicyDefinitionInner>, PolicyDefinitionInner>() {
              @Override
              public PolicyDefinitionInner call(ServiceResponse<PolicyDefinitionInner> response) {
                  return response.body();
              }
          });
      }
docs: Gets the policy definition at management group level.
  
  @param policyDefinitionName The name of the policy definition to get.
  @param managementGroupId The ID of the management group.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the PolicyDefinitionInner object