Fixes missing prompt template or system template (#2408)

* Fix issue #2402: Handle missing templates gracefully

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

* Fix import sorting in test files

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

* Bluit in top of devin-ai integration

* Fixed test cases

* Fixed test cases

* fixed linting issue

* Added docs

---------

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: Joe Moura <joao@crewai.com>

docs/concepts/agents.mdx

@@ -255,7 +255,11 @@ custom_agent = Agent(
 - `response_template`: Formats agent responses
 
 <Note>
-When using custom templates, you can use variables like `{role}`, `{goal}`, and `{input}` in your templates. These will be automatically populated during execution.
+When using custom templates, ensure that both `system_template` and `prompt_template` are defined. The `response_template` is optional but recommended for consistent output formatting.
+</Note>  
+
+<Note>
+When using custom templates, you can use variables like `{role}`, `{goal}`, and `{backstory}` in your templates. These will be automatically populated during execution.
 </Note>
 
 ## Agent Tools

src/crewai/utilities/prompts.py

@@ -54,10 +54,12 @@ class Prompts(BaseModel):
         response_template=None,
     ) -> str:
         """Constructs a prompt string from specified components."""
-        if not system_template and not prompt_template:
+        if not system_template or not prompt_template:
+            # If any of the required templates are missing, fall back to the default format
             prompt_parts = [self.i18n.slice(component) for component in components]
             prompt = "".join(prompt_parts)
         else:
+            # All templates are provided, use them
             prompt_parts = [
                 self.i18n.slice(component)
                 for component in components
@@ -67,8 +69,12 @@ class Prompts(BaseModel):
             prompt = prompt_template.replace(
                 "{{ .Prompt }}", "".join(self.i18n.slice("task"))
             )
-            response = response_template.split("{{ .Response }}")[0]
-            prompt = f"{system}\n{prompt}\n{response}"
+            # Handle missing response_template
+            if response_template:
+                response = response_template.split("{{ .Response }}")[0]
+                prompt = f"{system}\n{prompt}\n{response}"
+            else:
+                prompt = f"{system}\n{prompt}"
 
         prompt = (
             prompt.replace("{goal}", self.agent.goal)

tests/agent_test.py

@@ -72,9 +72,54 @@ def test_agent_creation():
     assert agent.role == "test role"
     assert agent.goal == "test goal"
     assert agent.backstory == "test backstory"
-    assert agent.tools == []
+
+def test_agent_with_only_system_template():
+    """Test that an agent with only system_template works without errors."""
+    agent = Agent(
+        role="Test Role",
+        goal="Test Goal",
+        backstory="Test Backstory",
+        allow_delegation=False,
+        system_template="You are a test agent...",
+        # prompt_template is intentionally missing
+    )
+
+    assert agent.role == "Test Role"
+    assert agent.goal == "Test Goal"
+    assert agent.backstory == "Test Backstory"
+
+def test_agent_with_only_prompt_template():
+    """Test that an agent with only system_template works without errors."""
+    agent = Agent(
+        role="Test Role",
+        goal="Test Goal",
+        backstory="Test Backstory",
+        allow_delegation=False,
+        prompt_template="You are a test agent...",
+        # prompt_template is intentionally missing
+    )
+
+    assert agent.role == "Test Role"
+    assert agent.goal == "Test Goal"
+    assert agent.backstory == "Test Backstory"
 
 
+def test_agent_with_missing_response_template():
+    """Test that an agent with system_template and prompt_template but no response_template works without errors."""
+    agent = Agent(
+        role="Test Role",
+        goal="Test Goal",
+        backstory="Test Backstory",
+        allow_delegation=False,
+        system_template="You are a test agent...",
+        prompt_template="This is a test prompt...",
+        # response_template is intentionally missing
+    )
+
+    assert agent.role == "Test Role"
+    assert agent.goal == "Test Goal"
+    assert agent.backstory == "Test Backstory"
+    
 def test_agent_default_values():
     agent = Agent(role="test role", goal="test goal", backstory="test backstory")
     assert agent.llm.model == "gpt-4o-mini"