Revert "throw error for empty asset key (#8069)" (#8093)

This reverts commit ac6007c. Some users still have rows with this property in their DBs, and these assets are now raising errors when the asset catalog is loaded.

We should also watch out for breaking changes to customers' existing write paths, although that one is more open to debate since its invalid data.

python_modules/dagster/dagster/core/definitions/events.py

@@ -87,9 +87,6 @@ def __new__(cls, path: Sequence[str]):
         else:
             path = list(check.sequence_param(path, "path", of_type=str))
 
-        check.invariant(
-            all(len(seg) > 0 for seg in path), "Asset key segments must be non-empty strings."
-        )
         return super(AssetKey, cls).__new__(cls, path=path)
 
     def __str__(self):

python_modules/dagster/dagster_tests/core_tests/storage_tests/test_assets.py

@@ -1,7 +1,4 @@
-import pytest
-
 from dagster import AssetKey, AssetMaterialization, Output, job, op
-from dagster._check import CheckError
 from dagster.core.definitions.events import parse_asset_key_string
 from dagster.core.events.log import EventLogEntry
 from dagster.core.instance import DagsterInstance, InstanceRef
@@ -10,13 +7,6 @@
 from dagster.utils.test import copy_directory
 
 
-def test_invalid_asset_key():
-    with pytest.raises(CheckError):
-        AssetKey("")
-    with pytest.raises(CheckError):
-        AssetKey(["foo", "", "bar"])
-
-
 def test_structured_asset_key():
     asset_parsed = AssetKey(parse_asset_key_string("(Hello)"))
     assert len(asset_parsed.path) == 1