Error message after pulling hyperspy upstream into @ZanettaPM's background branch

zanetta_after_pull_upstream

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-4-825396d5c1d6> in <module>()
----> 1 m.plot()

c:\users\me\documents\github\hyperspy\hyperspy\models\model1d.py in plot(self, plot_components, **kwargs)
    668         # Add the line to the figure
    669         _plot.signal_plot.add_line(l2)
--> 670         l2.plot()
    671         _plot.signal_plot.events.closed.connect(self._close_plot, [])
    672 

c:\users\me\documents\github\hyperspy\hyperspy\drawing\signal1d.py in plot(self, data, data_function_kwargs, norm)
    308         self.data_function_kwargs = data_function_kwargs
    309         self.norm = norm
--> 310         data = self._get_data()
    311         if self.line is not None:
    312             self.line.remove()

c:\users\me\documents\github\hyperspy\hyperspy\drawing\signal1d.py in _get_data(self, real_part)
    345         else:
    346             ydata = self.data_function(axes_manager=self.axes_manager,
--> 347                                        **self.data_function_kwargs).real
    348         return ydata
    349 

c:\users\me\documents\github\hyperspy\hyperspy\models\model1d.py in _model2plot(self, axes_manager, out_of_range2nans)
    631             self.axes_manager = axes_manager
    632             self.fetch_stored_values()
--> 633         s = self.__call__(non_convolved=False, onlyactive=True)
    634         if old_axes_manager is not None:
    635             self.axes_manager = old_axes_manager

c:\users\me\documents\github\hyperspy\hyperspy\models\model1d.py in __call__(self, non_convolved, onlyactive, component_list)
    408             sum_ = np.zeros(len(axis))
    409             for component in component_list:
--> 410                 sum_ += component.function(axis)
    411             to_return = sum_
    412 

c:\users\me\documents\github\hyperspy\hyperspy\_components\physical_background.py in function(self, x)
    279         Cthickness=self.coating_thickness.value
    280 
--> 281         Mu=Mucoef(self.model,self.quanti.value)
    282         Mu=np.array(Mu,dtype=float)
    283         #Mu=Mu[self.model.channel_switches]

c:\users\me\documents\github\hyperspy\hyperspy\_components\physical_background.py in Mucoef(model, quanti)
    145         t=t[model.channel_switches]
    146         u=t[0::5]
--> 147         Ac=mass_absorption_mixture(elements=model._signal.metadata.Sample.elements ,weight_percent=weight, energies=u)
    148         b=t
    149         Ac=np.interp(b,u,Ac) # Interpolation allows to gain some time

c:\users\me\documents\github\hyperspy\hyperspy\misc\material.py in _mass_absorption_mixture(weight_percent, elements, energies)
    354     Scattering Tables (version 2.1).
    355     """
--> 356     if len(elements) != len(weight_percent):
    357         raise ValueError(
    358             "Elements and weight_fraction should have the same length")

TypeError: object of type 'float' has no len()