Avoid confusing error when using axes and missing entities

openfisca_core/simulations/simulation_builder.py

@@ -294,12 +294,12 @@ def add_default_group_entity(self, persons_ids, entity):
         persons_count = len(persons_ids)
         self.entity_ids[entity.plural] = persons_ids
         self.entity_counts[entity.plural] = persons_count
-        self.memberships[entity.plural] = numpy.arange(
+        self.memberships[entity.plural] = list(numpy.arange(
             0, persons_count, dtype=numpy.int32
-        )
-        self.roles[entity.plural] = numpy.repeat(
+        ))
+        self.roles[entity.plural] = list(numpy.repeat(
             entity.flattened_roles[0], persons_count
-        )
+        ))
 
     def add_group_entity(self, persons_plural, persons_ids, entity, instances_json):
         """

tests/core/test_axes.py

@@ -350,3 +350,27 @@ def test_simulation_with_axes(tax_benefit_system):
         [0, 0, 0, 0, 0, 0]
     )
     assert simulation.get_array("rent", "2018-11") == pytest.approx([0, 0, 3000, 0])
+
+# Test for missing group entities with build_from_entities()
+
+def test_simulation_with_axes_missing_entities(tax_benefit_system):
+    input_yaml = """
+        persons:
+          Alicia: {salary: {2018-11: 0}}
+          Javier: {}
+          Tom: {}
+        axes:
+            -
+                - count: 2
+                  name: rent
+                  min: 0
+                  max: 3000
+                  period: 2018-11
+    """
+    data = test_runner.yaml.safe_load(input_yaml)
+    simulation = SimulationBuilder().build_from_entities(tax_benefit_system, data)
+    assert simulation.get_array("salary", "2018-11") == pytest.approx(
+        [0, 0, 0, 0, 0, 0]
+    )
+    # Since a household is synthesized for each person, we have six:
+    assert simulation.get_array("rent", "2018-11") == pytest.approx([0, 0, 0, 3000, 0, 0])