code: public Observable<String> beginReplaceContentAsync(String resourceGroupName, String automationAccountName, String runbookName, String runbookContent) {
          return beginReplaceContentWithServiceResponseAsync(resourceGroupName, automationAccountName, runbookName, runbookContent).map(new Func1<ServiceResponseWithHeaders<String, RunbookDraftReplaceContentHeaders>, String>() {
              @Override
              public String call(ServiceResponseWithHeaders<String, RunbookDraftReplaceContentHeaders> response) {
                  return response.body();
              }
          });
      }
docs: Replaces the runbook draft content.
  
  @param resourceGroupName Name of an Azure Resource group.
  @param automationAccountName The name of the automation account.
  @param runbookName The runbook name.
  @param runbookContent The runbook draft content.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the String object