additional params should be ingored. not force a blow up
the additional params on populations are meant to be for backends to have whatever they need. if the end user has added one we don't recognise (aka say a nest param) our code will currently blow about incorrect params for create vertex etc. 

the reason it was exposed was draft work for splitter objects
https://github.com/SpiNNakerManchester/sPyNNaker/pull/864

we should be able to just ignore them fully though. making the unexpected stuff redundant. 
diff --git a/spynnaker/pyNN/models/pynn_population_common.py b/spynnaker/pyNN/models/pynn_population_common.py
index de06723c12..4f8be9be49 100644
--- a/spynnaker/pyNN/models/pynn_population_common.py
+++ b/spynnaker/pyNN/models/pynn_population_common.py
@@ -100,7 +100,10 @@ class PyNNPopulationCommon(object):
                     "A population cannot have a negative or zero size.")
             population_parameters = dict(model.default_population_parameters)
             if additional_parameters is not None:
-                population_parameters.update(additional_parameters)
+                # check that the additions are suitable. report wrong ones
+                # and ignore
+                population_parameters = self._process_additional_params(
+                    additional_parameters, population_parameters)
             self.__vertex = model.create_vertex(
                 size, label, constraints, **population_parameters)
 
@@ -179,6 +182,17 @@ class PyNNPopulationCommon(object):
             for variable, value in iteritems(initial_values):
                 self._initialize(variable, value)
 
+    @staticmethod
+    def _process_additional_params(
+            additional_parameters, population_parameters):
+        for key in additional_parameters.keys():
+            if key in population_parameters:
+                population_parameters[key] = additional_parameters[key]
+            else:
+                logger.warning(
+                    "additional_parameter {} will be ignored".format(key))
+        return population_parameters
+
     @property
     def first_id(self):
         """ The ID of the first member of the population.
['spynnaker/pyNN/models/pynn_population_common.py']