feat: support to set an empty context to the Task

Author: lucasgomide

src/crewai/crew.py

@@ -52,7 +52,7 @@
 from crewai.tools.base_tool import BaseTool, Tool
 from crewai.types.usage_metrics import UsageMetrics
 from crewai.utilities import I18N, FileHandler, Logger, RPMController
-from crewai.utilities.constants import TRAINING_DATA_FILE
+from crewai.utilities.constants import EMPTY, TRAINING_DATA_FILE
 from crewai.utilities.evaluators.crew_evaluator_handler import CrewEvaluator
 from crewai.utilities.evaluators.task_evaluator import TaskEvaluator
 from crewai.utilities.events.crew_events import (
@@ -478,7 +478,7 @@ def validate_async_task_cannot_include_sequential_async_tasks_in_context(self):
         separated by a synchronous task.
         """
         for i, task in enumerate(self.tasks):
-            if task.async_execution and task.context:
+            if task.async_execution and isinstance(task.context, list):
                 for context_task in task.context:
                     if context_task.async_execution:
                         for j in range(i - 1, -1, -1):
@@ -496,7 +496,7 @@ def validate_context_no_future_tasks(self):
         task_indices = {id(task): i for i, task in enumerate(self.tasks)}
 
         for task in self.tasks:
-            if task.context:
+            if isinstance(task.context, list):
                 for context_task in task.context:
                     if id(context_task) not in task_indices:
                         continue  # Skip context tasks not in the main tasks list
@@ -1034,11 +1034,14 @@ def _update_manager_tools(
                 )
         return cast(List[BaseTool], tools)
 
-    def _get_context(self, task: Task, task_outputs: List[TaskOutput]):
+    def _get_context(self, task: Task, task_outputs: List[TaskOutput]) -> str:
+        if not task.context:
+            return ""
+
         context = (
-            aggregate_raw_outputs_from_tasks(task.context)
-            if task.context
-            else aggregate_raw_outputs_from_task_outputs(task_outputs)
+            aggregate_raw_outputs_from_task_outputs(task_outputs)
+            if task.context is EMPTY
+            else aggregate_raw_outputs_from_tasks(task.context)
         )
         return context
 
@@ -1226,7 +1229,7 @@ def copy(self):
             task_mapping[task.key] = cloned_task
 
         for cloned_task, original_task in zip(cloned_tasks, self.tasks):
-            if original_task.context:
+            if isinstance(original_task.context, list):
                 cloned_context = [
                     task_mapping[context_task.key]
                     for context_task in original_task.context

src/crewai/task.py

@@ -41,6 +41,7 @@
 from crewai.tasks.task_output import TaskOutput
 from crewai.tools.base_tool import BaseTool
 from crewai.utilities.config import process_config
+from crewai.utilities.constants import EMPTY
 from crewai.utilities.converter import Converter, convert_to_model
 from crewai.utilities.events import (
     TaskCompletedEvent,
@@ -97,7 +98,7 @@ class Task(BaseModel):
     )
     context: Optional[List["Task"]] = Field(
         description="Other tasks that will have their output used as context for this task.",
-        default=None,
+        default=EMPTY,
     )
     async_execution: Optional[bool] = Field(
         description="Whether the task should be executed asynchronously or not.",
@@ -643,7 +644,7 @@ def copy(
 
         cloned_context = (
             [task_mapping[context_task.key] for context_task in self.context]
-            if self.context
+            if isinstance(self.context, list)
             else None
         )
 

src/crewai/telemetry/telemetry.py

@@ -232,7 +232,7 @@ def operation():
                                 "agent_key": task.agent.key if task.agent else None,
                                 "context": (
                                     [task.description for task in task.context]
-                                    if task.context
+                                    if isinstance(task.context, list)
                                     else None
                                 ),
                                 "tools_names": [
@@ -748,7 +748,7 @@ def operation():
                             "agent_key": task.agent.key if task.agent else None,
                             "context": (
                                 [task.description for task in task.context]
-                                if task.context
+                                if isinstance(task.context, list)
                                 else None
                             ),
                             "tools_names": [

src/crewai/utilities/constants.py

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

src/crewai/utilities/formatter.py

@@ -1,5 +1,7 @@
 import re
-from typing import TYPE_CHECKING, List
+from typing import TYPE_CHECKING, List, Type
+
+from crewai.utilities.constants import EMPTY
 
 if TYPE_CHECKING:
     from crewai.task import Task
@@ -17,6 +19,11 @@ 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)