Raise error if dataset name empty (#1083)

* raise error if dataset name empty.

hidden dataset project when name is an empty string.

if the dataset project happens to match an existing project, it can be quite jarring to have one's history of results suddenly become hidden.

if there's an intent behind this behavior, please let me know and I'd gladly change it to a warning instead.

* move check to top of init, change message

* whitespace

clearml/datasets/dataset.py

@@ -159,6 +159,8 @@ class Dataset(object):
                 LoggerRoot.get_base_logger().warning(
                     "Setting non-semantic dataset version '{}'".format(self._dataset_version)
                 )
+        if dataset_name == "":
+            raise ValueError("`dataset_name` cannot be an empty string")
         if task:
             self._task_pinger = None
             self._created_task = False