IndexError while making NER using flair example with custom dataset

[MohamedLotfyElrefai]

Describe the bug
I have passed a train data file and empty files for dev and the test data set I face the same problem on my custom data set.
link for data set

https://drive.google.com/open?id=1ZiWTVuvcm5r0kRM50P8xV2trbKyjVU7-

To Reproduce

from flair.data import Corpus
from flair.datasets import ColumnCorpus

# define columns
columns = {0: 'text', 1: 'ner'}

# this is the folder in which train, test and dev files reside

# init a corpus using column format, data folder and the names of the train, dev and test files
corpus: Corpus = ColumnCorpus('',columns,
                              train_file='train.txt',
                              dev_file='test.txt',
                             test_file='test.txt')

from flair.data import Corpus
from flair.embeddings import TokenEmbeddings, WordEmbeddings, StackedEmbeddings, PooledFlairEmbeddings
from typing import List

# 1. get the corpus

# 2. what tag do we want to predict?
tag_type = 'ner'

# 3. make the tag dictionary from the corpus
tag_dictionary = corpus.make_tag_dictionary(tag_type=tag_type)

# initialize embeddings
embedding_types: List[TokenEmbeddings] = [

    # GloVe embeddings
    WordEmbeddings('glove'),

    # contextual string embeddings, forward
    PooledFlairEmbeddings('news-forward', pooling='min'),

    # contextual string embeddings, backward
    PooledFlairEmbeddings('news-backward', pooling='min'),
]

embeddings: StackedEmbeddings = StackedEmbeddings(embeddings=embedding_types)

# initialize sequence tagger
from flair.models import SequenceTagger

tagger: SequenceTagger = SequenceTagger(hidden_size=256,
                                        embeddings=embeddings,
                                        tag_dictionary=tag_dictionary,
                                        tag_type=tag_type)

# initialize trainer
from flair.trainers import ModelTrainer

trainer: ModelTrainer = ModelTrainer(tagger,corpus)

trainer.train('resources/taggers/example-ner',train_with_dev=True,max_epochs=150)

Expected behavior
IndexError: string index out of range

Environment (please complete the following information):

• OS [Linux 18.04 ]:
• Version [flair-0.4.3]:
• cuda 10 and gpu version
  OS [windows10 ]:
• Version [flair-0.4.3]:
• cpu