diff --git a/mara_pipelines/incremental_processing/processed_files.py b/mara_pipelines/incremental_processing/processed_files.py
index fd04915..69a983e 100644
--- a/mara_pipelines/incremental_processing/processed_files.py
+++ b/mara_pipelines/incremental_processing/processed_files.py
@@ -74,4 +74,5 @@ def already_processed_file(node_path: str, file_name: str) -> datetime:
 FROM data_integration_processed_file WHERE node_path = {'%s'}
 AND file_name = {'%s'}
 """, (node_path, file_name,))
-        return cursor.fetchone()[0]
\ No newline at end of file
+        row = cursor.fetchone()
+        return row[0] if row else None
\ No newline at end of file
diff --git a/mara_pipelines/parallel_tasks/files.py b/mara_pipelines/parallel_tasks/files.py
index be43fd6..8ae6d13 100644
--- a/mara_pipelines/parallel_tasks/files.py
+++ b/mara_pipelines/parallel_tasks/files.py
@@ -55,7 +55,14 @@ def __init__(self, id: str, description: str, file_pattern: str, read_mode: Read
         self._db_alias = db_alias
         self.timezone = timezone
 
-        self.use_workers = self.read_mode == [ReadMode.ALL, ReadMode.ONLY_NEW, ReadMode.ONLY_CHANGED]
+        self.use_workers = self.read_mode in [ReadMode.ALL] # NOTE: It should be possible to implement here ReadMode.ONLY_NEW
+                                                            #       and ReadMode.ONLY_CHANGED as well. I tried it but run into
+                                                            #        issues with the lambda function used in `process_commands`:
+                                                            #
+                                                            #       The commands passed via `feed_workers` are processed through a
+                                                            #       multiprocessing.Queue. Probably all objects/functions passed over
+                                                            #       there need to be declared on root level. See as well:
+                                                            #       https://stackoverflow.com/a/8805244
 
     @property
     def db_alias(self):
diff --git a/mara_pipelines/pipelines.py b/mara_pipelines/pipelines.py
index 24d01f8..39259d1 100644
--- a/mara_pipelines/pipelines.py
+++ b/mara_pipelines/pipelines.py
@@ -137,6 +137,7 @@ def run(self):
                     raise ValueError(f"Unexecpted type passed to command_queue: {value}")
 
                 for command in commands:
+                    command.parent = self
                     if not command.run():
                         return False
 
diff --git a/tests/test_parallel_read.py b/tests/test_parallel_read.py
index 696be9b..bc8d3f7 100644
--- a/tests/test_parallel_read.py
+++ b/tests/test_parallel_read.py
@@ -25,7 +25,7 @@ def empty_files():
     root_path = EMPTY_FILES_BASE_PATH
     root_path.mkdir(parents=True, exist_ok=True)
 
-    file_list = [str((root_path / str(file)).absolute()) for file in range(1, 8*3)]
+    file_list = [str((root_path / str(file)).absolute()) for file in range(25)]
 
     # create empty files
     for file in file_list:
@@ -64,6 +64,7 @@ def test_read_mode_all(empty_files):
             description="Runs a test pipeline which checks if a file exist",
             file_pattern='*',
             read_mode=ReadMode.ALL,
-            target_table=None))
+            target_table=None,
+            max_number_of_parallel_tasks=4))
 
     run_pipeline(pipeline)
\ No newline at end of file