We are currently solving the following issue within our repository. Here is the issue text:
--- BEGIN ISSUE ---
[DataFrame] Error checking on Pandas version
We need better reporting for issues with the Pandas version on a user's system. 

--- END ISSUE ---

Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
--- BEGIN FILES ---
Path: `python/ray/dataframe/__init__.py`
Content:
```
1 from __future__ import absolute_import
2 from __future__ import division
3 from __future__ import print_function
4 import threading
5 
6 DEFAULT_NPARTITIONS = 4
7 
8 
9 def set_npartition_default(n):
10     global DEFAULT_NPARTITIONS
11     DEFAULT_NPARTITIONS = n
12 
13 
14 def get_npartitions():
15     return DEFAULT_NPARTITIONS
16 
17 
18 # We import these file after above two function
19 # because they depend on npartitions.
20 from .dataframe import DataFrame  # noqa: 402
21 from .dataframe import from_pandas  # noqa: 402
22 from .dataframe import to_pandas  # noqa: 402
23 from .series import Series  # noqa: 402
24 from .io import (read_csv, read_parquet)  # noqa: 402
25 
26 __all__ = [
27     "DataFrame", "from_pandas", "to_pandas", "Series", "read_csv",
28     "read_parquet"
29 ]
30 
31 try:
32     if threading.current_thread().name == "MainThread":
33         import ray
34         ray.init()
35 except AssertionError:
36     pass
37
```
--- END FILES ---

Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.

Here is an example:

```diff
diff --git a/examples/server_async.py b/examples/server_async.py
--- a/examples/server_async.py
+++ b/examples/server_async.py
@@ -313,4 +313,4 @@
 
 
 if __name__ == "__main__":
-    asyncio.run(run_async_server("."), debug=True)
+    asyncio.run(run_async_server(), debug=True)
diff --git a/examples/server_sync.py b/examples/server_sync.py
--- a/examples/server_sync.py
+++ b/examples/server_sync.py
@@ -313,5 +313,5 @@
 
 
 if __name__ == "__main__":
-    server = run_sync_server(".")
+    server = run_sync_server()
     server.shutdown()

```

diff --git a/python/ray/dataframe/__init__.py b/python/ray/dataframe/__init__.py
--- a/python/ray/dataframe/__init__.py
+++ b/python/ray/dataframe/__init__.py
@@ -1,8 +1,18 @@
 from __future__ import absolute_import
 from __future__ import division
 from __future__ import print_function
+
+import pandas as pd
 import threading
 
+pd_version = pd.__version__
+pd_major = int(pd_version.split(".")[0])
+pd_minor = int(pd_version.split(".")[1])
+
+if pd_major == 0 and pd_minor < 22:
+    raise Exception("In order to use Pandas on Ray, please upgrade your Pandas"
+                    " version to >= 0.22.")
+
 DEFAULT_NPARTITIONS = 4

{"golden_diff": "diff --git a/python/ray/dataframe/__init__.py b/python/ray/dataframe/__init__.py\n--- a/python/ray/dataframe/__init__.py\n+++ b/python/ray/dataframe/__init__.py\n@@ -1,8 +1,18 @@\n from __future__ import absolute_import\n from __future__ import division\n from __future__ import print_function\n+\n+import pandas as pd\n import threading\n \n+pd_version = pd.__version__\n+pd_major = int(pd_version.split(\".\")[0])\n+pd_minor = int(pd_version.split(\".\")[1])\n+\n+if pd_major == 0 and pd_minor < 22:\n+    raise Exception(\"In order to use Pandas on Ray, please upgrade your Pandas\"\n+                    \" version to >= 0.22.\")\n+\n DEFAULT_NPARTITIONS = 4\n", "issue": "[DataFrame] Error checking on Pandas version\nWe need better reporting for issues with the Pandas version on a user's system. \n", "before_files": [{"content": "from __future__ import absolute_import\nfrom __future__ import division\nfrom __future__ import print_function\nimport threading\n\nDEFAULT_NPARTITIONS = 4\n\n\ndef set_npartition_default(n):\n    global DEFAULT_NPARTITIONS\n    DEFAULT_NPARTITIONS = n\n\n\ndef get_npartitions():\n    return DEFAULT_NPARTITIONS\n\n\n# We import these file after above two function\n# because they depend on npartitions.\nfrom .dataframe import DataFrame  # noqa: 402\nfrom .dataframe import from_pandas  # noqa: 402\nfrom .dataframe import to_pandas  # noqa: 402\nfrom .series import Series  # noqa: 402\nfrom .io import (read_csv, read_parquet)  # noqa: 402\n\n__all__ = [\n    \"DataFrame\", \"from_pandas\", \"to_pandas\", \"Series\", \"read_csv\",\n    \"read_parquet\"\n]\n\ntry:\n    if threading.current_thread().name == \"MainThread\":\n        import ray\n        ray.init()\nexcept AssertionError:\n    pass\n", "path": "python/ray/dataframe/__init__.py"}], "after_files": [{"content": "from __future__ import absolute_import\nfrom __future__ import division\nfrom __future__ import print_function\n\nimport pandas as pd\nimport threading\n\npd_version = pd.__version__\npd_major = int(pd_version.split(\".\")[0])\npd_minor = int(pd_version.split(\".\")[1])\n\nif pd_major == 0 and pd_minor < 22:\n    raise Exception(\"In order to use Pandas on Ray, please upgrade your Pandas\"\n                    \" version to >= 0.22.\")\n\nDEFAULT_NPARTITIONS = 4\n\n\ndef set_npartition_default(n):\n    global DEFAULT_NPARTITIONS\n    DEFAULT_NPARTITIONS = n\n\n\ndef get_npartitions():\n    return DEFAULT_NPARTITIONS\n\n\n# We import these file after above two function\n# because they depend on npartitions.\nfrom .dataframe import DataFrame  # noqa: 402\nfrom .dataframe import from_pandas  # noqa: 402\nfrom .dataframe import to_pandas  # noqa: 402\nfrom .series import Series  # noqa: 402\nfrom .io import (read_csv, read_parquet)  # noqa: 402\n\n__all__ = [\n    \"DataFrame\", \"from_pandas\", \"to_pandas\", \"Series\", \"read_csv\",\n    \"read_parquet\"\n]\n\ntry:\n    if threading.current_thread().name == \"MainThread\":\n        import ray\n        ray.init()\nexcept AssertionError:\n    pass\n", "path": "python/ray/dataframe/__init__.py"}]}