Facebook graph api 使用FBGraph检索Fb post注释

我试图检索Fb对特定帖子的评论。我尝试实现以下方法：

FbGraphResponse *fb_graph_response = [fbGraph doGraphPost1:@"3788106577940/comments" withPostVars1:[[NSDictionary alloc]initWithObjectsAndKeys:@"Hello",@"Hi", nil]];  
    SBJSON *parser = [[SBJSON alloc] init];
    NSDictionary *facebook_response = [parser objectWithString:fb_graph_response.htmlResponse error:nil];   
    //[parser release];

    //let's save the 'id' Facebook gives us so we can delete it if the user presses the 'delete /me/feed button'
    self.feedPostId = (NSString *)[facebook_response objectForKey:@"id"];
    NSLog(@"feedPostId, %@", feedPostId);

但我得到了以下错误：

 <CFBasicHash 0x6a64360 [0x1751b38]>{type = mutable dict, count = 1,
entries =>
    11 : <CFString 0x6a64e30 [0x1751b38]>{contents = "error"} = <CFBasicHash 0x6a64170 [0x1751b38]>{type = mutable dict, count = 3,
entries =>
    2 : <CFString 0x6a64410 [0x1751b38]>{contents = "type"} = <CFString 0x6a645f0 [0x1751b38]>{contents = "OAuthException"}
    3 : <CFString 0x6a64590 [0x1751b38]>{contents = "message"} = <CFString 0x6a644f0 [0x1751b38]>{contents = "(#1705) : You cannot make blank posts. Please enter some text and try again."}
    6 : <CFString 0x6a64200 [0x1751b38]>{contents = "code"} = 1705
}

}

请帮忙。谢谢

[fbGraph authenticateUserWithCallbackObject:self andSelector:@selector(fbGraphCallback) 
                         andExtendedPermissions:@"user_photos,user_videos,publish_stream,offline_access,user_checkins,friends_checkins,read_stream"];