Improve handling of null values in argument lists to the serviceJourn…

…eys graphQL method in the Transmodel API (#6375)

* Improves handling of null members in lists of arguments to the serviceJourneys GraphQL method.

With this change the null members are simply ignored, just like when passing null members to the ID list.

* Improves naming of utility function.

application/src/main/java/org/opentripplanner/apis/transmodel/TransmodelGraphQLSchema.java

@@ -9,6 +9,7 @@
 import static org.opentripplanner.apis.transmodel.model.EnumTypes.MULTI_MODAL_MODE;
 import static org.opentripplanner.apis.transmodel.model.EnumTypes.TRANSPORT_MODE;
 import static org.opentripplanner.apis.transmodel.model.scalars.DateTimeScalarFactory.createMillisecondsSinceEpochAsDateTimeStringScalar;
+import static org.opentripplanner.apis.transmodel.support.GqlUtil.toListNullSafe;
 import static org.opentripplanner.model.projectinfo.OtpProjectInfo.projectInfo;
 
 import graphql.Scalars;
@@ -1310,11 +1311,11 @@ private GraphQLSchema create() {
             );
             var privateCodes = FilterValues.ofEmptyIsEverything(
               "privateCodes",
-              environment.<List<String>>getArgument("privateCodes")
+              toListNullSafe(environment.<List<String>>getArgument("privateCodes"))
             );
             var activeServiceDates = FilterValues.ofEmptyIsEverything(
               "activeDates",
-              environment.<List<LocalDate>>getArgument("activeDates")
+              toListNullSafe(environment.<List<LocalDate>>getArgument("activeDates"))
             );
 
             TripRequest tripRequest = TripRequest

application/src/main/java/org/opentripplanner/apis/transmodel/support/GqlUtil.java

@@ -6,8 +6,11 @@
 import graphql.schema.GraphQLInputObjectField;
 import graphql.schema.GraphQLList;
 import graphql.schema.GraphQLNonNull;
+import java.util.Collection;
 import java.util.List;
 import java.util.Locale;
+import java.util.Objects;
+import javax.annotation.Nullable;
 import org.opentripplanner.apis.transmodel.TransmodelRequestContext;
 import org.opentripplanner.apis.transmodel.mapping.TransitIdMapper;
 import org.opentripplanner.framework.graphql.GraphQLUtils;
@@ -18,7 +21,7 @@
 
 /**
  * Provide some of the commonly used "chain" of methods. Like all ids should be created the same
- * wayThis
+ * way.
  */
 public class GqlUtil {
 
@@ -96,4 +99,15 @@ public static Locale getLocale(DataFetchingEnvironment environment) {
       ? GraphQLUtils.getLocale(environment, lang)
       : GraphQLUtils.getLocale(environment);
   }
+
+  /**
+   * Null-safe handling of a collection of type T. Returns an empty list if the collection is null.
+   * Null elements are filtered out.
+   */
+  public static <T> List<T> toListNullSafe(@Nullable Collection<T> args) {
+    if (args == null) {
+      return List.of();
+    }
+    return args.stream().filter(Objects::nonNull).toList();
+  }
 }