TSK-476 fix DB2 unittest errors

lib/taskana-core/src/main/java/pro/taskana/impl/TaskServiceImpl.java

@@ -550,17 +550,26 @@ public class TaskServiceImpl implements TaskService {
 
         // query for existing tasks. use taskMapper.findExistingTasks because this method
         // returns only the required information.
-        List<MinimalTaskSummary> taskSummaries = taskMapper.findExistingTasks(taskIds);
+        List<MinimalTaskSummary> taskSummaries;
-
+        if (taskIds.isEmpty()) {
+            taskSummaries = new ArrayList<>();
+        } else {
+            taskSummaries = taskMapper.findExistingTasks(taskIds);
+        }
         // check source WB (read)+transfer
         Set<String> workbasketIds = new HashSet<>();
         taskSummaries.stream().forEach(t -> workbasketIds.add(t.getWorkbasketId()));
         WorkbasketQueryImpl query = (WorkbasketQueryImpl) workbasketService.createWorkbasketQuery();
         query.setUsedToAugmentTasks(true);
-        List<WorkbasketSummary> sourceWorkbaskets = query
+        List<WorkbasketSummary> sourceWorkbaskets;
+        if (taskSummaries.isEmpty()) {
+            sourceWorkbaskets = new ArrayList<>();
+        } else {
+            sourceWorkbaskets = query
                 .callerHasPermission(WorkbasketPermission.TRANSFER)
                 .idIn(workbasketIds.toArray(new String[0]))
                 .list();
+        }
         taskIdIterator = taskIds.iterator();
         while (taskIdIterator.hasNext()) {
             String currentTaskId = taskIdIterator.next();

lib/taskana-core/src/main/java/pro/taskana/mappings/TaskMonitorMapper.java

@@ -208,37 +208,37 @@ public interface TaskMonitorMapper {
         @Param("customFieldValues") List<String> customFieldValues);
 
     @Select("<script>"
-        + "SELECT TASK.ID FROM TASKANA.TASK "
+        + "SELECT T.ID FROM TASKANA.TASK T "
         + "<if test=\"joinWithAttachments\">"
-        + "LEFT JOIN TASKANA.ATTACHMENT ON TASK.ID = ATTACHMENT.TASK_ID "
+        + "LEFT JOIN TASKANA.ATTACHMENT A ON T.ID = A.TASK_ID "
         + "</if>"
         + "<where>"
         + "<if test=\"workbasketIds != null\">"
-        + "TASK.WORKBASKET_ID IN (<foreach collection='workbasketIds' item='workbasketId' separator=','>#{workbasketId}</foreach>) "
+        + "T.WORKBASKET_ID IN (<foreach collection='workbasketIds' item='workbasketId' separator=','>#{workbasketId}</foreach>) "
         + "</if>"
         + "<if test=\"states != null\">"
-        + "AND TASK.STATE IN (<foreach collection='states' item='state' separator=','>#{state}</foreach>) "
+        + "AND T.STATE IN (<foreach collection='states' item='state' separator=','>#{state}</foreach>) "
         + "</if>"
         + "<if test=\"categories != null\">"
-        + "AND TASK.CLASSIFICATION_CATEGORY IN (<foreach collection='categories' item='category' separator=','>#{category}</foreach>) "
+        + "AND T.CLASSIFICATION_CATEGORY IN (<foreach collection='categories' item='category' separator=','>#{category}</foreach>) "
         + "</if>"
         + "<if test=\"domains != null\">"
         + "AND DOMAIN IN (<foreach collection='domains' item='domain' separator=','>#{domain}</foreach>) "
         + "</if>"
         + "<if test='classificationIds != null'>"
-        + "AND TASK.CLASSIFICATION_ID IN (<foreach collection='classificationIds' item='classificationId' separator=','>#{classificationId}</foreach>) "
+        + "AND T.CLASSIFICATION_ID IN (<foreach collection='classificationIds' item='classificationId' separator=','>#{classificationId}</foreach>) "
         + "</if>"
         + "<if test='excludedClassificationIds != null'>"
-        + "AND TASK.CLASSIFICATION_ID NOT IN (<foreach collection='excludedClassificationIds' item='excludedClassificationId' separator=','>#{excludedClassificationId}</foreach>) "
+        + "AND T.CLASSIFICATION_ID NOT IN (<foreach collection='excludedClassificationIds' item='excludedClassificationId' separator=','>#{excludedClassificationId}</foreach>) "
         + "</if>"
         + "<if test=\"customField != null and customFieldValues != null\">"
-        + "AND TASK.${customField}  IN (<foreach collection='customFieldValues' item='customFieldValue' separator=','>#{customFieldValue}</foreach>) "
+        + "AND T.${customField}  IN (<foreach collection='customFieldValues' item='customFieldValue' separator=','>#{customFieldValue}</foreach>) "
         + "</if>"
-        + "AND TASK.DUE IS NOT NULL AND ( "
+        + "AND T.DUE IS NOT NULL AND ( "
         + "<foreach collection='selectedItems' item='selectedItem' separator=' OR '>"
-        + "#{selectedItem.key} = TASK.${groupedBy} AND "
+        + "#{selectedItem.key} = T.${groupedBy} AND "
         + "<if test=\"joinWithAttachments\">"
-        + "ATTACHMENT.CLASSIFICATION_KEY = #{selectedItem.subKey} AND "
+        + "A.CLASSIFICATION_KEY = #{selectedItem.subKey} AND "
         + "</if>"
         + "<if test=\"_databaseId == 'db2'\">"
         + "#{selectedItem.upperAgeLimit} >= (DAYS(DUE) - DAYS(CURRENT_TIMESTAMP)) AND "