ValueError: too many values to unpack in metropolis sampling

when running pm.find_MAP, I got a missing input error:

---------------------------------------------------------------------------
MissingInputError                         Traceback (most recent call last)
<ipython-input-47-c454f54202c3> in <module>
 15 
 16 with model:
---> 17     pm.find_MAP()
 18     pm.sample(2000, step = pm.Metropolis())
 19 # def plot_result():

~/anaconda3/envs/Bayesian/lib/python3.6/site-packages/pymc3/tuning/starting.py in find_MAP(start, vars, method, return_raw, include_transformed, progressbar, maxeval, model, *args, **kwargs)
 81     start = Point(start, model=model)
 82     bij = DictToArrayBijection(ArrayOrdering(vars), start)
---> 83     logp_func = bij.mapf(model.fastlogp_nojac)
 84     x0 = bij.map(start)
 85 

~/anaconda3/envs/Bayesian/lib/python3.6/site-packages/pymc3/model.py in fastlogp_nojac(self)
244     @property
245     def fastlogp_nojac(self):
--> 246         return self.model.fastfn(self.logp_nojact)
247 
248     def fastdlogp_nojac(self, vars=None):

~/anaconda3/envs/Bayesian/lib/python3.6/site-packages/pymc3/model.py in fastfn(self, outs, mode, *args, **kwargs)
938         Compiled Theano function as point function.
939         """
--> 940         f = self.makefn(outs, mode, *args, **kwargs)
941         return FastPointFunc(f)
942 

~/anaconda3/envs/Bayesian/lib/python3.6/site-packages/pymc3/model.py in makefn(self, outs, mode, *args, **kwargs)
908                                    on_unused_input='ignore',
909                                    accept_inplace=True,
--> 910                                    mode=mode, *args, **kwargs)
911 
912     def fn(self, outs, mode=None, *args, **kwargs):

~/anaconda3/envs/Bayesian/lib/python3.6/site-packages/theano/compile/function.py in function(inputs, outputs, mode, updates, givens, no_default_updates, accept_inplace, name, rebuild_strict, allow_input_downcast, profile, on_unused_input)
315                    on_unused_input=on_unused_input,
316                    profile=profile,
--> 317                    output_keys=output_keys)
318     return fn

~/anaconda3/envs/Bayesian/lib/python3.6/site-packages/theano/compile/pfunc.py in pfunc(params, outputs, mode, updates, givens, no_default_updates, accept_inplace, name, rebuild_strict, allow_input_downcast, profile, on_unused_input, output_keys)
484                          accept_inplace=accept_inplace, name=name,
485                          profile=profile, on_unused_input=on_unused_input,
--> 486                          output_keys=output_keys)
487 
488 

~/anaconda3/envs/Bayesian/lib/python3.6/site-packages/theano/compile/function_module.py in    orig_function(inputs, outputs, mode, accept_inplace, name, profile, on_unused_input, output_keys)
   1837                   on_unused_input=on_unused_input,
   1838                   output_keys=output_keys,
-> 1839                   name=name)
   1840         with theano.change_flags(compute_test_value="off"):
   1841             fn = m.create(defaults)

~/anaconda3/envs/Bayesian/lib/python3.6/site-packages/theano/compile/function_module.py in __init__(self, inputs, outputs, mode, accept_inplace, function_builder, profile, on_unused_input, fgraph, output_keys, name)
   1485             # OUTPUT VARIABLES)
   1486             fgraph, additional_outputs = std_fgraph(inputs, outputs,
    -> 1487                                                     accept_inplace)
   1488             fgraph.profile = profile
   1489         else:

~/anaconda3/envs/Bayesian/lib/python3.6/site-packages/theano/compile/function_module.py in std_fgraph(input_specs, output_specs, accept_inplace)
179 
180     fgraph = gof.fg.FunctionGraph(orig_inputs, orig_outputs,
--> 181                                   update_mapping=update_mapping)
182 
183     for node in fgraph.apply_nodes:

~/anaconda3/envs/Bayesian/lib/python3.6/site-packages/theano/gof/fg.py in __init__(self, inputs, outputs, features, clone, update_mapping)
173 
174         for output in outputs:
--> 175             self.__import_r__(output, reason="init")
176         for i, output in enumerate(outputs):
177             output.clients.append(('output', i))

~/anaconda3/envs/Bayesian/lib/python3.6/site-packages/theano/gof/fg.py in __import_r__(self, variable, reason)
344         # Imports the owners of the variables
345         if variable.owner and variable.owner not in self.apply_nodes:
--> 346                 self.__import__(variable.owner, reason=reason)
347         elif (variable.owner is None and
348                 not isinstance(variable, graph.Constant) and

~/anaconda3/envs/Bayesian/lib/python3.6/site-packages/theano/gof/fg.py in __import__(self, apply_node, check, reason)
389                                      "for more information on this error."
390                                      % (node.inputs.index(r), str(node)))
  --> 391                         raise MissingInputError(error_msg, variable=r)
392 
393         for node in new_nodes:

MissingInputError: Input 0 of the graph (indices start from 0), used to compute Subtensor{int64}(euler_0, Constant{1}), was not provided and not given a value. Use the Theano flag exception_verbosity=‘high’, for more information on this error.