Fix issue #2402: Handle missing templates gracefully

Co-Authored-By: Joe Moura <joao@crewai.com>

test_fix_2402.py

@@ -0,0 +1,42 @@
+# test_fix_2402.py
+from crewai import Agent, Task, Crew
+
+# Case 1: Only system_template provided
+agent1 = Agent(
+    role="Test Role",
+    goal="Test Goal",
+    backstory="Test Backstory",
+    system_template="You are a test agent...",
+    # prompt_template is intentionally missing
+)
+
+# Case 2: system_template and prompt_template provided, but response_template missing
+agent2 = Agent(
+    role="Test Role",
+    goal="Test Goal",
+    backstory="Test Backstory",
+    system_template="You are a test agent...",
+    prompt_template="This is a test prompt...",
+    # response_template is intentionally missing
+)
+
+# Create tasks and crews
+task1 = Task(description="Test task 1", agent=agent1, expected_output="Test output 1")
+task2 = Task(description="Test task 2", agent=agent2, expected_output="Test output 2")
+
+crew1 = Crew(agents=[agent1], tasks=[task1])
+crew2 = Crew(agents=[agent2], tasks=[task2])
+
+print("Testing agent with only system_template...")
+try:
+    agent1.execute_task(task1)
+    print("Success! No error was raised.")
+except Exception as e:
+    print(f"Error: {e}")
+
+print("\nTesting agent with missing response_template...")
+try:
+    agent2.execute_task(task2)
+    print("Success! No error was raised.")
+except Exception as e:
+    print(f"Error: {e}")