Fix flairNLP#565 by raising an Exception for an empty String (flairNL…

…P#566)

* Fix flairNLP#565 by raising ValueError for empty string

* Added unit test for empty string case in PR flairNLP#566

flair/data.py

@@ -323,6 +323,9 @@ def __init__(self, text: str = None, use_tokenizer: bool = False, labels: Union[
 
             # otherwise assumes whitespace tokenized text
             else:
+                # catch the empty string case
+                if not text:
+                    raise ValueError("Cannot convert empty string to a Sentence object.")
                 # add each word in tokenized string as Token object to Sentence
                 word = ''
                 for index, char in enumerate(text):

tests/test_data.py

@@ -22,6 +22,13 @@ def test_get_head():
     assert (token1 == token2.get_head())
     assert (None == token1.get_head())
 
+def test_create_sentence_on_empty_string():
+
+    with pytest.raises(ValueError) as e:
+        sentence: Sentence = Sentence('')
+
+        assert (e.type is ValueError)
+        assert (e.value.args[0] == "Cannot convert empty string to a Sentence object.")
 
 def test_create_sentence_without_tokenizer():
     sentence: Sentence = Sentence('I love Berlin.')