[BUG] [GPU Error Bug] SELECT (CASE <string> WHEN <column> THEN <column> ELSE <string> END ) FROM <table> JOIN <table> brings Error

[qwebug]

What happened:

SELECT (CASE <string> WHEN <column> THEN <column> ELSE <string> END ) FROM <table> JOIN <table> brings error, when using GPU execution.

However it is able to output result, when using CPU execution.

What you expected to happen:

It will not bring error, when using GPU execution.

Minimal Complete Verifiable Example:

import pandas as pd
import dask.dataframe as dd
from dask_sql import Context

c = Context()

df0 = pd.DataFrame({
    'c0': [3231.0000],
})
t0 = dd.from_pandas(df0, npartitions=1)
c.create_table('t0', t0, gpu=False)
c.create_table('t0_gpu', t0, gpu=True)

df1 = pd.DataFrame({
    'c0': [1537.0000],
})
t1 = dd.from_pandas(df1, npartitions=1)
c.create_table('t1', t1, gpu=False)
c.create_table('t1_gpu', t1, gpu=True)

df2 = pd.DataFrame({
    'c0': [''],
    'c1': ["DATE '2008-11-25'"],
})
t2 = dd.from_pandas(df2, npartitions=1)
c.create_table('t2', t2, gpu=False)
c.create_table('t2_gpu', t2, gpu=True)

print('CPU Result:')
result1= c.sql("SELECT (CASE '1' WHEN t2.c1 THEN t2.c0 ELSE '' END ) FROM t1, t0 LEFT JOIN t2 ON (true)").compute()
print(result1)

print('GPU Result:')
result2= c.sql("SELECT (CASE '1' WHEN t2_gpu.c1 THEN t2_gpu.c0 ELSE '' END ) FROM t1_gpu, t0_gpu LEFT JOIN t2_gpu ON (true)").compute()
print(result2)

Result:

INFO:numba.cuda.cudadrv.driver:init
CPU Result:
  CASE Utf8("1") WHEN t2.c1 THEN t2.c0 ELSE Utf8("") END
0                                                       
GPU Result:
Traceback (most recent call last):
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/dask/dataframe/utils.py", line 193, in raise_on_meta_error
    yield
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/dask/dataframe/core.py", line 6793, in _emulate
    return func(*_extract_meta(args, True), **_extract_meta(kwargs, True))
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/dask/utils.py", line 1105, in __call__
    return getattr(__obj, self.method)(*args, **kwargs)
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/nvtx/nvtx.py", line 101, in inner
    result = func(*args, **kwargs)
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/cudf/core/series.py", line 3504, in where
    result_col = super().where(cond, other, inplace)
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/nvtx/nvtx.py", line 101, in inner
    result = func(*args, **kwargs)
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/cudf/core/single_column_frame.py", line 434, in where
    input_col, other = _check_and_cast_columns_with_other(
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/cudf/core/_internals/where.py", line 84, in _check_and_cast_columns_with_other
    if _is_non_decimal_numeric_dtype(source_dtype) and _can_cast(
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/cudf/utils/dtypes.py", line 680, in _can_cast
    return np.can_cast(from_dtype, to_dtype)
  File "<__array_function__ internals>", line 200, in can_cast
TypeError: did not understand one of the types; 'None' not accepted

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/tmp/test.py", line 34, in <module>
    result2= c.sql("SELECT (CASE '1' WHEN t2_gpu.c1 THEN t2_gpu.c0 ELSE '' END ) FROM t1_gpu, t0_gpu LEFT JOIN t2_gpu ON (true)").compute()
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/dask_sql/context.py", line 513, in sql
    return self._compute_table_from_rel(rel, return_futures)
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/dask_sql/context.py", line 839, in _compute_table_from_rel
    dc = RelConverter.convert(rel, context=self)
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/dask_sql/physical/rel/convert.py", line 61, in convert
    df = plugin_instance.convert(rel, context=context)
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/dask_sql/physical/rel/logical/project.py", line 57, in convert
    new_columns[random_name] = RexConverter.convert(
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/dask_sql/physical/rex/convert.py", line 74, in convert
    df = plugin_instance.convert(rel, rex, dc, context=context)
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/dask_sql/physical/rex/core/call.py", line 1129, in convert
    return operation(*operands, **kwargs)
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/dask_sql/physical/rex/core/call.py", line 77, in __call__
    return self.f(*operands, **kwargs)
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/dask_sql/physical/rex/core/call.py", line 221, in case
    return then.where(where, other=other)
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/dask/dataframe/core.py", line 3349, in where
    return map_partitions(M.where, self, cond, other, enforce_metadata=False)
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/dask/dataframe/core.py", line 6863, in map_partitions
    meta = _get_meta_map_partitions(args, dfs, func, kwargs, meta, parent_meta)
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/dask/dataframe/core.py", line 6974, in _get_meta_map_partitions
    meta = _emulate(func, *args, udf=True, **kwargs)
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/dask/dataframe/core.py", line 6792, in _emulate
    with raise_on_meta_error(funcname(func), udf=udf), check_numeric_only_deprecation():
  File "/opt/conda/envs/rapids/lib/python3.10/contextlib.py", line 153, in __exit__
    self.gen.throw(typ, value, traceback)
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/dask/dataframe/utils.py", line 214, in raise_on_meta_error
    raise ValueError(msg) from e
ValueError: Metadata inference failed in `where`.

You have supplied a custom function and Dask is unable to 
determine the type of output that that function returns. 

To resolve this please provide a meta= keyword.
The docstring of the Dask function you ran should have more information.

Original error is below:
------------------------
TypeError("did not understand one of the types; 'None' not accepted")

Traceback:
---------
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/dask/dataframe/utils.py", line 193, in raise_on_meta_error
    yield
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/dask/dataframe/core.py", line 6793, in _emulate
    return func(*_extract_meta(args, True), **_extract_meta(kwargs, True))
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/dask/utils.py", line 1105, in __call__
    return getattr(__obj, self.method)(*args, **kwargs)
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/nvtx/nvtx.py", line 101, in inner
    result = func(*args, **kwargs)
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/cudf/core/series.py", line 3504, in where
    result_col = super().where(cond, other, inplace)
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/nvtx/nvtx.py", line 101, in inner
    result = func(*args, **kwargs)
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/cudf/core/single_column_frame.py", line 434, in where
    input_col, other = _check_and_cast_columns_with_other(
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/cudf/core/_internals/where.py", line 84, in _check_and_cast_columns_with_other
    if _is_non_decimal_numeric_dtype(source_dtype) and _can_cast(
  File "/opt/conda/envs/rapids/lib/python3.10/site-packages/cudf/utils/dtypes.py", line 680, in _can_cast
    return np.can_cast(from_dtype, to_dtype)
  File "<__array_function__ internals>", line 200, in can_cast

Anything else we need to know?:

Environment:

• dask-sql version: 2023.6.0
• Python version: Python 3.10.11
• Operating System: Ubuntu22.04
• Install method (conda, pip, source): Docker deploy by https://hub.docker.com/layers/rapidsai/rapidsai-dev/23.06-cuda11.8-devel-ubuntu22.04-py3.10/images/sha256-cfbb61fdf7227b090a435a2e758114f3f1c31872ed8dbd96e5e564bb5fd184a7?context=explore