feat: support to set an empty context to the Task (#2793)

* feat: support to set an empty context to the Task

* sytle: fix linter issues

src/crewai/utilities/constants.py

@@ -5,3 +5,14 @@ KNOWLEDGE_DIRECTORY = "knowledge"
 MAX_LLM_RETRY = 3
 MAX_FILE_NAME_LENGTH = 255
 EMITTER_COLOR = "bold_blue"
+
+
+class _NotSpecified:
+    def __repr__(self):
+        return "NOT_SPECIFIED"
+
+
+# Sentinel value used to detect when no value has been explicitly provided.
+# Unlike `None`, which might be a valid value from the user, `NOT_SPECIFIED` allows
+# us to distinguish between "not passed at all" and "explicitly passed None" or "[]".
+NOT_SPECIFIED = _NotSpecified()

src/crewai/utilities/formatter.py

@@ -1,6 +1,6 @@
-import re
 from typing import TYPE_CHECKING, List
 
+
 if TYPE_CHECKING:
     from crewai.task import Task
     from crewai.tasks.task_output import TaskOutput
@@ -17,6 +17,11 @@ def aggregate_raw_outputs_from_task_outputs(task_outputs: List["TaskOutput"]) ->
 
 def aggregate_raw_outputs_from_tasks(tasks: List["Task"]) -> str:
     """Generate string context from the tasks."""
-    task_outputs = [task.output for task in tasks if task.output is not None]
+
+    task_outputs = (
+        [task.output for task in tasks if task.output is not None]
+        if isinstance(tasks, list)
+        else []
+    )
 
     return aggregate_raw_outputs_from_task_outputs(task_outputs)