diff --git a/api/core/app/apps/workflow/app_runner.py b/api/core/app/apps/workflow/app_runner.py
index b43daa8a15..4d368136ca 100644
--- a/api/core/app/apps/workflow/app_runner.py
+++ b/api/core/app/apps/workflow/app_runner.py
@@ -82,7 +82,6 @@ class WorkflowAppRunner(WorkflowBasedAppRunner):
                 workflow=workflow,
                 node_id=self.application_generate_entity.single_iteration_run.node_id,
                 user_inputs=self.application_generate_entity.single_iteration_run.inputs,
-                variable_loader=self._var_loader,
             )
         elif self.application_generate_entity.single_loop_run:
             # if only single loop run is requested
diff --git a/api/core/workflow/entities/node_entities.py b/api/core/workflow/entities/node_entities.py
index 82fd6cdc30..df7d19cb75 100644
--- a/api/core/workflow/entities/node_entities.py
+++ b/api/core/workflow/entities/node_entities.py
@@ -1,4 +1,4 @@
-from collections.abc import Mapping
+from collections.abc import Mapping, MutableMapping
 from enum import StrEnum
 from typing import Any, Optional
 
@@ -43,7 +43,7 @@ class NodeRunResult(BaseModel):
     inputs: Optional[Mapping[str, Any]] = None  # node inputs
     process_data: Optional[Mapping[str, Any]] = None  # process data
     outputs: Optional[Mapping[str, Any]] = None  # node outputs
-    metadata: Optional[Mapping[NodeRunMetadataKey, Any]] = None  # node metadata
+    metadata: Optional[MutableMapping[NodeRunMetadataKey, Any]] = None  # node metadata
     llm_usage: Optional[LLMUsage] = None  # llm usage
 
     edge_source_handle: Optional[str] = None  # source handle id of node with multiple branches
diff --git a/api/core/workflow/nodes/llm/file_saver.py b/api/core/workflow/nodes/llm/file_saver.py
index c85baade03..a4b45ce652 100644
--- a/api/core/workflow/nodes/llm/file_saver.py
+++ b/api/core/workflow/nodes/llm/file_saver.py
@@ -119,9 +119,6 @@ class FileSaverImpl(LLMFileSaver):
             size=len(data),
             related_id=tool_file.id,
             url=url,
-            # TODO(QuantumGhost): how should I set the following key?
-            # What's the difference between `remote_url` and `url`?
-            # What's the purpose of `storage_key` and `dify_model_identity`?
             storage_key=tool_file.file_key,
         )
 
diff --git a/api/core/workflow/nodes/loop/loop_node.py b/api/core/workflow/nodes/loop/loop_node.py
index 088c003d3e..f6a12d60c1 100644
--- a/api/core/workflow/nodes/loop/loop_node.py
+++ b/api/core/workflow/nodes/loop/loop_node.py
@@ -478,7 +478,7 @@ class LoopNode(BaseNode[LoopNodeData]):
 
             variable_mapping.update(sub_node_variable_mapping)
 
-        for loop_variable in node_data.loop_variables:
+        for loop_variable in node_data.loop_variables or []:
             if loop_variable.value_type == "variable":
                 assert loop_variable.value is not None, "Loop variable value must be provided for variable type"
                 # add loop variable to variable mapping
diff --git a/api/core/workflow/variable_loader.py b/api/core/workflow/variable_loader.py
index 4e9bedb41e..4648a9b752 100644
--- a/api/core/workflow/variable_loader.py
+++ b/api/core/workflow/variable_loader.py
@@ -1,5 +1,5 @@
 import abc
-from collections.abc import Mapping
+from collections.abc import Mapping, Sequence
 from typing import Any, Protocol
 
 from core.variables import Variable
@@ -55,7 +55,7 @@ DUMMY_VARIABLE_LOADER = _DummyVariableLoader()
 def load_into_variable_pool(
     variable_loader: VariableLoader,
     variable_pool: VariablePool,
-    variable_mapping: Mapping[str, list[str]],
+    variable_mapping: Mapping[str, Sequence[str]],
     user_inputs: Mapping[str, Any],
 ):
     # Loading missing variable from draft var here, and set it into
diff --git a/api/libs/gen_utils.py b/api/libs/gen_utils.py
index e457176187..012c48b09f 100644
--- a/api/libs/gen_utils.py
+++ b/api/libs/gen_utils.py
@@ -1,31 +1,11 @@
 """Utility functions for working with generators."""
 
-import logging
 from collections.abc import Callable, Generator
-from inspect import isgenerator
 from typing import TypeVar
 
 _YieldT = TypeVar("_YieldT")
 _YieldR = TypeVar("_YieldR")
 
-_T = TypeVar("_T")
-
-
-def inspect(gen_or_normal: _T, logger: logging.Logger) -> _T:
-    if not isgenerator(gen_or_normal):
-        return gen_or_normal
-
-    def wrapper():
-        for item in gen_or_normal:
-            logger.info(
-                "received generator item, type=%s, value=%s",
-                type(item),
-                item,
-            )
-            yield item
-
-    return wrapper()
-
 
 def map_(
     gen: Generator[_YieldT, None, None],
diff --git a/api/services/workflow_service.py b/api/services/workflow_service.py
index 8a71fcf3aa..87ba69c4dd 100644
--- a/api/services/workflow_service.py
+++ b/api/services/workflow_service.py
@@ -459,7 +459,6 @@ class WorkflowService:
     ) -> NodeExecution:
         try:
             node_instance, generator = invoke_node_fn()
-            generator = gen_utils.inspect(generator, logging.getLogger(__name__))
 
             node_run_result: NodeRunResult | None = None
             for event in generator: