AttributeError: ‘NoneType‘ object has no attribute ‘get_fetch_list‘

import paddle.fluid as fluid
 
x1 = fluid.layers.fill_constant(shape=[2,2], value=1, dtype='int64')
x2 = fluid.layers.fill_constant(shape=[2,2], value=1, dtype='int64')
 
y1 = fluid.layers.sum(x=[x1,x2])
 
 
place = fluid.CPUPlace()
exe = fluid.executor.Executor(place)
exe.run(fluid.default_startup_program())
result = exe.run(program=fluid.default_main_program(), fetch_list=[y1])
print(result)

PS C:\Users\timwang> python -u "d:\学习\AI\paddle\constant_sum.py"
C:\Users\timwang\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.10_qbz5n2kfra8p0\LocalCache\local-packages\Python310\site-packages\paddle\fluid\executor.py:1350: UserWarning: There are no operators in the program to be executed. If you pass Program manually, please use fluid.program_guard to ensure the current Program is being used.
  warnings.warn(error_info)
Traceback (most recent call last):
  File "d:\学习\AI\paddle\constant_sum.py", line 11, in 
    exe.run(fluid.default_startup_program())
  File "C:\Users\timwang\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.10_qbz5n2kfra8p0\LocalCache\local-packages\Python310\site-packages\paddle\fluid\executor.py", line 1299, in run
    six.reraise(*sys.exc_info())
  File "C:\Users\timwang\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.10_qbz5n2kfra8p0\LocalCache\local-packages\Python310\site-packages\six.py", line 719, in reraise
    raise value
  File "C:\Users\timwang\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.10_qbz5n2kfra8p0\LocalCache\local-packages\Python310\site-packages\paddle\fluid\executor.py", line 1285, in run
    res = self._run_impl(
  File "C:\Users\timwang\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.10_qbz5n2kfra8p0\LocalCache\local-packages\Python310\site-packages\paddle\fluid\executor.py", line 1510, in _run_impl
    return self._run_program(
  File "C:\Users\timwang\AppData\Local\Packages\PythonSoftwareFoundation.Python.3.10_qbz5n2kfra8p0\LocalCache\local-packages\Python310\site-packages\paddle\fluid\executor.py", line 1612, in _run_program
    arr = scope.find_var(fetch_var_name).get_fetch_list()
AttributeError: 'NoneType' object has no attribute 'get_fetch_list'

这个问题是版本问题，转为以下版本就没有问题了

python：3.7 

paddle： 2.0.0a0