运行线性回归训练的例子时，报如下错误，求助

/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/paddle/fluid/executor.py:789: UserWarning: The following exception is not an EOF exception.
"The following exception is not an EOF exception.")

---------------------------------------------------------------------------EnforceNotMet Traceback (most recent call last) in
3 train_cost = exe.run(program=fluid.default_main_program(),
4 feed={'x': x_data, 'y': y_data},
----> 5 fetch_list=[avg_cost])
6 print("Pass:%d, Cost:%0.5f" % (pass_id, train_cost[0]))
/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/paddle/fluid/executor.py in run(self, program, feed, fetch_list, feed_var_name, fetch_var_name, scope, return_numpy, use_program_cache)
788 warnings.warn(
789 "The following exception is not an EOF exception.")
--> 790 six.reraise(*sys.exc_info())
791
792 def _run_impl(self, program, feed, fetch_list, feed_var_name,
/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/six.py in reraise(tp, value, tb)
691 if value.__traceback__ is not tb:
692 raise value.with_traceback(tb)
--> 693 raise value
694 finally:
695 value = None
/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/paddle/fluid/executor.py in run(self, program, feed, fetch_list, feed_var_name, fetch_var_name, scope, return_numpy, use_program_cache)
783 scope=scope,
784 return_numpy=return_numpy,
--> 785 use_program_cache=use_program_cache)
786 except Exception as e:
787 if not isinstance(e, core.EOFException):
/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/paddle/fluid/executor.py in _run_impl(self, program, feed, fetch_list, feed_var_name, fetch_var_name, scope, return_numpy, use_program_cache)
836 scope=scope,
837 return_numpy=return_numpy,
--> 838 use_program_cache=use_program_cache)
839
840 program._compile(scope, self.place)
/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/paddle/fluid/executor.py in _run_program(self, program, feed, fetch_list, feed_var_name, fetch_var_name, scope, return_numpy, use_program_cache)
910 if not use_program_cache:
911 self._default_executor.run(program.desc, scope, 0, True, True,
--> 912 fetch_var_name)
913 else:
914 self._default_executor.run_prepared_ctx(ctx, scope, False, False,
EnforceNotMet:

--------------------------------------------
C++ Call Stacks (More useful to developers):
--------------------------------------------
0 std::string paddle::platform::GetTraceBackString(std::string const&, char const*, int)
1 paddle::platform::EnforceNotMet::EnforceNotMet(std::string const&, char const*, int)
2 paddle::operators::SumOp::GetExpectedKernelType(paddle::framework::ExecutionContext const&) const
3 paddle::framework::OperatorWithKernel::ChooseKernel(paddle::framework::RuntimeContext const&, paddle::framework::Scope const&, paddle::platform::Place const&) const
4 paddle::framework::OperatorWithKernel::RunImpl(paddle::framework::Scope const&, paddle::platform::Place const&, paddle::framework::RuntimeContext*) const
5 paddle::framework::OperatorWithKernel::RunImpl(paddle::framework::Scope const&, paddle::platform::Place const&) const
6 paddle::framework::OperatorBase::Run(paddle::framework::Scope const&, paddle::platform::Place const&)
7 paddle::framework::Executor::RunPreparedContext(paddle::framework::ExecutorPrepareContext*, paddle::framework::Scope*, bool, bool, bool)
8 paddle::framework::Executor::Run(paddle::framework::ProgramDesc const&, paddle::framework::Scope*, int, bool, bool, std::vector > const&, bool, bool)

------------------------------------------
Python Call Stacks (More useful to users):
------------------------------------------
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/paddle/fluid/framework.py", line 2525, in append_op
attrs=kwargs.get("attrs", None))
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/paddle/fluid/layer_helper.py", line 43, in append_op
return self.main_program.current_block().append_op(*args, **kwargs)
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/paddle/fluid/layers/nn.py", line 9836, in sum
attrs={'use_mkldnn': False})
File "", line 2, in
y = fluid.layers.sum(x=[a, b])
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/IPython/core/interactiveshell.py", line 3265, in run_code
exec(code_obj, self.user_global_ns, self.user_ns)
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/IPython/core/interactiveshell.py", line 3183, in run_ast_nodes
if (yield from self.run_code(code, result)):
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/IPython/core/interactiveshell.py", line 3018, in run_cell_async
interactivity=interactivity, compiler=compiler, result=result)
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/IPython/core/async_helpers.py", line 67, in _pseudo_sync_runner
coro.send(None)
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/IPython/core/interactiveshell.py", line 2843, in _run_cell
return runner(coro)
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/IPython/core/interactiveshell.py", line 2817, in run_cell
raw_cell, store_history, silent, shell_futures)
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/ipykernel/zmqshell.py", line 536, in run_cell
return super(ZMQInteractiveShell, self).run_cell(*args, **kwargs)
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/ipykernel/ipkernel.py", line 294, in do_execute
res = shell.run_cell(code, store_history=store_history, silent=silent)
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/tornado/gen.py", line 326, in wrapper
yielded = next(result)
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/ipykernel/kernelbase.py", line 534, in execute_request
user_expressions, allow_stdin,
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/tornado/gen.py", line 326, in wrapper
yielded = next(result)
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/ipykernel/kernelbase.py", line 267, in dispatch_shell
yield gen.maybe_future(handler(stream, idents, msg))
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/tornado/gen.py", line 326, in wrapper
yielded = next(result)
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/ipykernel/kernelbase.py", line 357, in process_one
yield gen.maybe_future(dispatch(*args))
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/tornado/gen.py", line 1147, in run
yielded = self.gen.send(value)
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/tornado/gen.py", line 1080, in __init__
self.run()
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/tornado/gen.py", line 346, in wrapper
runner = Runner(result, future, yielded)
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/ipykernel/kernelbase.py", line 370, in dispatch_queue
yield self.process_one()
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/tornado/gen.py", line 1147, in run
yielded = self.gen.send(value)
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/tornado/gen.py", line 1233, in inner
self.run()
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/tornado/stack_context.py", line 300, in null_wrapper
return fn(*args, **kwargs)
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/tornado/ioloop.py", line 758, in _run_callback
ret = callback()
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/asyncio/events.py", line 88, in _run
self._context.run(self._callback, *self._args)
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/asyncio/base_events.py", line 1771, in _run_once
handle._run()
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/asyncio/base_events.py", line 534, in run_forever
self._run_once()
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/tornado/platform/asyncio.py", line 132, in start
self.asyncio_loop.run_forever()
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/ipykernel/kernelapp.py", line 505, in start
self.io_loop.start()
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/traitlets/config/application.py", line 664, in launch_instance
app.start()
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/site-packages/ipykernel_launcher.py", line 16, in
app.launch_new_instance()
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/runpy.py", line 85, in _run_code
exec(code, run_globals)
File "/opt/conda/envs/python35-paddle120-env/lib/python3.7/runpy.py", line 193, in _run_module_as_main
"__main__", mod_spec)

----------------------
Error Message Summary:
----------------------
Error: Sum operator should have at least one tensor
[Hint: Expected dtype != -1, but received dtype:-1 == -1:-1.] at (/paddle/paddle/fluid/operators/sum_op.cc:142)
[operator < sum > error]