Handle the case with no test data populators (#122)

Since there is no populator yet Spring fails when trying to inject since it does not support empty collections. Mark the dependency as optional until we have at least one populator at which point we can simply the code again.

Reviewed-on: #122
Reviewed-by: Nico Athanassiadis <nico@dsv.su.se>
Co-authored-by: Andreas Svanberg <andreass@dsv.su.se>
Co-committed-by: Andreas Svanberg <andreass@dsv.su.se>

test-data/src/main/java/se/su/dsv/scipro/testdata/DataInitializer.java

@@ -42,7 +42,7 @@ public class DataInitializer implements Lifecycle, BaseData, Factory {
     public static final long RESEARCH_AREA_ID = 12L;
 
     @Inject
-    private Collection<TestDataPopulator> testDataPopulators = new ArrayList<>();
+    private Optional<Collection<TestDataPopulator>> testDataPopulators = Optional.empty();
 
     @Inject
     private UserService userService;
@@ -123,7 +123,8 @@ public class DataInitializer implements Lifecycle, BaseData, Factory {
             createTarget();
             createStudentIdea();
             createRoughDraftApproval();
-            for (TestDataPopulator testDataPopulator : testDataPopulators) {
+            Collection<TestDataPopulator> availablePopulators = testDataPopulators.orElseGet(Collections::emptySet);
+            for (TestDataPopulator testDataPopulator : availablePopulators) {
                 testDataPopulator.populate(this, this);
             }
         }