flutter can't import lpinyin.dart，error as below:

Try correcting the name to the name of an existing getter, or defining a getter or field named 'PinyinHelper'. String pinyin = PinyinHelper.getPinyinE(user.userName); ^^^^^^^^^^^^ Unhandled exception: FileSystemException(uri=org-dartlang-untranslatable-uri:package%3Alpinyin%2Flpinyin.dart; message=StandardFileSystem only supports file:* and data:* URIs) #0 StandardFileSystem.entityForUri (package:front_end/src/api_prototype/standard_file_system.dart:33:7)

#1 asFileUri (package:vm/kernel_front_end.dart:601:37) #2
FrontendCompiler._outputDependenciesDelta (package:vm/frontend_server.dart:401:39) #3 FrontendCompiler.compile (package:vm/frontend_server.dart:375: 13) #4 _FlutterFrontendCompiler.compile (package:frontend_ser ver/server.dart:31:22) #5 starter (package:frontend_server/s erver.dart:128:27) #6 main (file:///C:/b/s/w/ir/k/src/flutter/frontend_ser ver/bin/starter.dart:8:30) #7 _startIsolate. ( dart:isolate-patch/isolate_patch.dart:299:32) #8 _RawReceivePortImpl._handleMessage (dart:i solate-patch/isolate_patch.dart:172:12)

像 "a,b" 这种会报错，中间是英文逗号，我试了中文逗号，句号，英文句号等都可以，唯独英文逗号不行，这么什么问题？

The following RangeError was thrown while handling a gesture: RangeError (index): Invalid value: Valid value range is empty: 0

When the exception was thrown, this was the stack: #0 _StringBase.[] (dart:core-patch/string_patch.dart:252:55) #1 PinyinHelper.getShortPinyin. (package:lpinyin/src/pinyin_helper.dart:51:21)

demo:

import 'package:lpinyin/lpinyin.dart';

main() {
  print(PinyinHelper.getPinyin('李四',separator: ''));
  print(PinyinHelper.getPinyin('小李',separator: ''));
  print(PinyinHelper.getPinyin('王五',separator: ''));
}

output:

李si
xiaoli
wangwu

separator为""的情况下，拼音会少了最后一个字母

return (sb.toString().endsWith(separator) ? sb.toString().substring(0, sb.toString().length - 1) : sb.toString());