diff --git a/README.md b/README.md
index d45ebc4..f0c2a93 100644
--- a/README.md
+++ b/README.md
@@ -65,10 +65,10 @@ For instance, Rasa requires a `.tar.gz` format trained model in the
 - [x] [Rasa](https://rasa.com/) intents/entities classifier (to use Rasa, please install it with `pip install -e ".[rasa]"`)
 - [ ] [Watson Assistant](https://www.ibm.com/products/watson-assistant) intents/entities classifier -- Planned
 
-**NOTE**: To use OpenAI GPT models don't forget to add your `OPEN_API_KEY` in a `.env` file under your project folder. 
-The `.env` file should look like:
+**NOTE**: To use OpenAI GPT models don't forget to add the `OPEN_API_KEY` environment
+variable with:
 ```bash
-OPENAI_API_KEY=your_api_key
+export OPENAI_API_KEY=your_api_key
 ```
 
 ## Write your own Engine
@@ -119,7 +119,11 @@ ltl_formulas = translate(utterance, engine=my_engine, filter=my_filter)
 Contributions are welcome! Here's how to set up the development environment:
 - set up your preferred virtualenv environment
 - clone the repo: `git clone https://github.com/IBM/nl2ltl.git && cd nl2ltl`
+- install dependencies: `pip install -e .`
 - install dev dependencies: `pip install -e ".[dev]"`
+- install pre-commit: `pre-commit install`
+- sign-off your commits using the `-s` flag in the commit message to be compliant with 
+the [DCO](https://developercertificate.org/)
 
 ## Tests
 
diff --git a/nl2ltl/filters/simple_filters.py b/nl2ltl/filters/simple_filters.py
index 506b40d..65ae13c 100644
--- a/nl2ltl/filters/simple_filters.py
+++ b/nl2ltl/filters/simple_filters.py
@@ -3,6 +3,7 @@
 
 from pylogics.syntax.base import Formula
 
+from nl2ltl.declare.base import Template
 from nl2ltl.filters.base import Filter
 from nl2ltl.filters.utils.conflicts import conflicts
 from nl2ltl.filters.utils.subsumptions import subsumptions
@@ -44,7 +45,7 @@ def enforce(output: Dict[Formula, float], entities: Dict[str, float], **kwargs)
         """
         result_set = set()
 
-        highest_scoring_formula = max(output, key=output.get)
+        highest_scoring_formula = max(output, key=output.get, default=Template)
         formula_conflicts = conflicts(highest_scoring_formula)
         formula_subsumptions = subsumptions(highest_scoring_formula)
 
diff --git a/tests/conftest.py b/tests/conftest.py
index 0e2ff51..ca9ca9b 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -13,8 +13,8 @@
 
 class UtterancesFixtures:
     utterances = [
-        "whenever I get a Slack, send a Gmail",
-        "Invite Sales employees to Thursday's meeting",
-        "If a new Eventbrite is created, alert me through Slack",
-        "send me a Slack whenever I get a Gmail",
+        "whenever I get a Slack, send a Gmail.",
+        "Invite Sales employees.",
+        "If a new Eventbrite is created, alert me through Slack.",
+        "send me a Slack whenever I get a Gmail.",
     ]
diff --git a/tests/test_gpt.py b/tests/test_gpt.py
index 643bfa6..841e13a 100644
--- a/tests/test_gpt.py
+++ b/tests/test_gpt.py
@@ -4,7 +4,7 @@
 import pytest
 
 from nl2ltl import translate
-from nl2ltl.engines.gpt.core import GPTEngine, Models
+from nl2ltl.engines.gpt.core import GPTEngine
 from nl2ltl.filters.simple_filters import BasicFilter, GreedyFilter
 
 from .conftest import UtterancesFixtures
@@ -18,7 +18,7 @@ def setup_class(cls):
         """Setup any state specific to the execution of the given class (which
         usually contains tests).
         """
-        cls.gpt_engine = GPTEngine(model=Models.GPT35_INSTRUCT.value)
+        cls.gpt_engine = GPTEngine()
         cls.basic_filter = BasicFilter()
         cls.greedy_filter = GreedyFilter()
 
diff --git a/tox.ini b/tox.ini
index 7c3febc..906f448 100644
--- a/tox.ini
+++ b/tox.ini
@@ -35,7 +35,7 @@ commands = ruff check .
 
 [testenv:ruff-check-apply]
 skip_install = True
-deps = ruff==0.1.9r
+deps = ruff==0.1.9
 commands = ruff check --fix --show-fixes .
 
 [testenv:ruff-format]