code: def create_package(self, assay=None, mass=0.0, normalise=True):
          
  
          if assay is None:
              return MaterialPackage(self, self.create_empty_assay())
  
          if normalise:
              assay_total = self.get_assay_total(assay)
          else:
              assay_total = 1.0
          return MaterialPackage(self, mass * self.assays[assay] / assay_total)
docs: Create a MaterialPackage based on the specified parameters.
  
          :param assay: The name of the assay based on which the package must be
            created.
          :param mass: [kg] The mass of the package.
          :param normalise: Indicates whether the assay must be normalised before
            creating the package.
  
          :returns: The created MaterialPackage.