diff --git a/.github/workflows/pytest.yml b/.github/workflows/pytest.yml
index a4c27116..af98e210 100644
--- a/.github/workflows/pytest.yml
+++ b/.github/workflows/pytest.yml
@@ -43,4 +43,4 @@ jobs:
           uv pip freeze --system
 
       - name: Run tests
-        run: pytest --cov=pyerrors -vv
+        run: pytest --cov=pyerrors -vv -Werror
diff --git a/examples/06_gevp.ipynb b/examples/06_gevp.ipynb
index 3e6c12d5..3de14d5e 100644
--- a/examples/06_gevp.ipynb
+++ b/examples/06_gevp.ipynb
@@ -151,7 +151,7 @@
     "\n",
     "$$C_{\\textrm{projected}}(t)=v_1^T \\underline{C}(t) v_2$$\n",
     "\n",
-    "If we choose the vectors to be $v_1=v_2=(0,1,0,0)$, we should get the same correlator as in the cell above. \n",
+    "If we choose the vectors to be $v_1=v_2=(1,0,0,0)$, we should get the same correlator as in the cell above. \n",
     "\n",
     "Thinking about it this way is usefull in the Context of the generalized eigenvalue problem (GEVP), used to find the source-sink combination, which best describes a certain energy eigenstate.\n",
     "A good introduction is found in https://arxiv.org/abs/0902.1265."
diff --git a/pyerrors/input/json.py b/pyerrors/input/json.py
index a0d3304a..a2008f9c 100644
--- a/pyerrors/input/json.py
+++ b/pyerrors/input/json.py
@@ -571,7 +571,6 @@ def _ol_from_dict(ind, reps='DICTOBS'):
     counter = 0
 
     def dict_replace_obs(d):
-        nonlocal ol
         nonlocal counter
         x = {}
         for k, v in d.items():
@@ -592,7 +591,6 @@ def _ol_from_dict(ind, reps='DICTOBS'):
         return x
 
     def list_replace_obs(li):
-        nonlocal ol
         nonlocal counter
         x = []
         for e in li:
@@ -613,7 +611,6 @@ def _ol_from_dict(ind, reps='DICTOBS'):
         return x
 
     def obslist_replace_obs(li):
-        nonlocal ol
         nonlocal counter
         il = []
         for e in li:
@@ -694,7 +691,6 @@ def _od_from_list_and_dict(ol, ind, reps='DICTOBS'):
 
     def dict_replace_string(d):
         nonlocal counter
-        nonlocal ol
         x = {}
         for k, v in d.items():
             if isinstance(v, dict):
@@ -710,7 +706,6 @@ def _od_from_list_and_dict(ol, ind, reps='DICTOBS'):
 
     def list_replace_string(li):
         nonlocal counter
-        nonlocal ol
         x = []
         for e in li:
             if isinstance(e, list):
diff --git a/pyerrors/input/pandas.py b/pyerrors/input/pandas.py
index 13482983..af446cfc 100644
--- a/pyerrors/input/pandas.py
+++ b/pyerrors/input/pandas.py
@@ -1,6 +1,7 @@
 import warnings
 import gzip
 import sqlite3
+from contextlib import closing
 import pandas as pd
 from ..obs import Obs
 from ..correlators import Corr
@@ -29,9 +30,8 @@ def to_sql(df, table_name, db, if_exists='fail', gz=True, **kwargs):
     None
     """
     se_df = _serialize_df(df, gz=gz)
-    con = sqlite3.connect(db)
-    se_df.to_sql(table_name, con, if_exists=if_exists, index=False, **kwargs)
-    con.close()
+    with closing(sqlite3.connect(db)) as con:
+        se_df.to_sql(table_name, con=con, if_exists=if_exists, index=False, **kwargs)
 
 
 def read_sql(sql, db, auto_gamma=False, **kwargs):
@@ -52,9 +52,8 @@ def read_sql(sql, db, auto_gamma=False, **kwargs):
     data : pandas.DataFrame
         Dataframe with the content of the sqlite database.
     """
-    con = sqlite3.connect(db)
-    extract_df = pd.read_sql(sql, con, **kwargs)
-    con.close()
+    with closing(sqlite3.connect(db)) as con:
+        extract_df = pd.read_sql(sql, con=con, **kwargs)
     return _deserialize_df(extract_df, auto_gamma=auto_gamma)
 
 
diff --git a/pyerrors/version.py b/pyerrors/version.py
index d0979fd0..806254b1 100644
--- a/pyerrors/version.py
+++ b/pyerrors/version.py
@@ -1 +1 @@
-__version__ = "2.14.0"
+__version__ = "2.15.0-dev"
diff --git a/setup.py b/setup.py
index 76efe7e2..8c42f4a6 100644
--- a/setup.py
+++ b/setup.py
@@ -30,7 +30,6 @@ setup(name='pyerrors',
       classifiers=[
           'Development Status :: 5 - Production/Stable',
           'Intended Audience :: Science/Research',
-          'License :: OSI Approved :: MIT License',
           'Programming Language :: Python :: 3',
           'Programming Language :: Python :: 3.9',
           'Programming Language :: Python :: 3.10',