diff --git a/.github/workflows/pre-commit.yml b/.github/workflows/pre-commit.yml
index 9e52050..ad89a90 100644
--- a/.github/workflows/pre-commit.yml
+++ b/.github/workflows/pre-commit.yml
@@ -5,6 +5,6 @@ jobs:
   lint:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
-      - uses: actions/setup-python@v3
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
       - uses: pre-commit/action@v3.0.0
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 5be678a..9ec7ecc 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -1,11 +1,11 @@
 repos:
   - repo: https://github.com/psf/black
-    rev: 23.11.0
+    rev: 24.4.2
     hooks:
     - id: black
       language_version: python3
   - repo: https://github.com/pycqa/flake8
-    rev: 6.1.0
+    rev: 7.1.0
     hooks:
     - id: flake8
       language_version: python3
diff --git a/unseen/bootstrap.py b/unseen/bootstrap.py
index ee20f66..4271dc0 100644
--- a/unseen/bootstrap.py
+++ b/unseen/bootstrap.py
@@ -68,12 +68,17 @@ def random_resample(
             )
         ]
         args_sub = [
-            xr.concat(
-                [obj.isel({dim: random_sample}) for random_sample in random_samples],
-                dim=dim,
+            (
+                xr.concat(
+                    [
+                        obj.isel({dim: random_sample})
+                        for random_sample in random_samples
+                    ],
+                    dim=dim,
+                )
+                if dim in obj.dims
+                else obj
             )
-            if dim in obj.dims
-            else obj
             for obj in args_sub
         ]
 
diff --git a/unseen/eva.py b/unseen/eva.py
index 975cbce..921c29b 100644
--- a/unseen/eva.py
+++ b/unseen/eva.py
@@ -357,7 +357,7 @@ def _fit(
     covariate = _format_covariate(data, covariate, stationary, core_dim)
 
     # Input core dimensions
-    if hasattr(covariate, core_dim):
+    if core_dim is not None and hasattr(covariate, core_dim):
         # Covariate has the same core dimension as data
         input_core_dims = [[core_dim], [core_dim]]
     else:
diff --git a/unseen/fileio.py b/unseen/fileio.py
index 7e168cb..3a0cd4a 100644
--- a/unseen/fileio.py
+++ b/unseen/fileio.py
@@ -456,10 +456,8 @@ def _fix_metadata(ds, metadata_file):
 
     if "rename" in metadata_dict:
         for orig_var, target_var in metadata_dict["rename"].items():
-            try:
+            if orig_var in ds:
                 ds = ds.rename({orig_var: target_var})
-            except ValueError:
-                pass
 
     if "drop_coords" in metadata_dict:
         for drop_coord in metadata_dict["drop_coords"]:
@@ -472,7 +470,8 @@ def _fix_metadata(ds, metadata_file):
 
     if "units" in metadata_dict:
         for var, units in metadata_dict["units"].items():
-            ds[var].attrs["units"] = units
+            if var in ds.data_vars:
+                ds[var].attrs["units"] = units
 
     return ds