From 9e8f7600624b43269f31f3cb569011ea907c8841 Mon Sep 17 00:00:00 2001
From: j-atkins <106238905+j-atkins@users.noreply.github.com>
Date: Tue, 3 Mar 2026 09:07:57 +0100
Subject: [PATCH 1/4] handle null for instruments

---
 src/virtualship/utils.py | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/virtualship/utils.py b/src/virtualship/utils.py
index cef83501..627bd5ec 100644
--- a/src/virtualship/utils.py
+++ b/src/virtualship/utils.py
@@ -15,8 +15,8 @@
 import numpy as np
 import pyproj
 import xarray as xr
-from parcels import FieldSet
 
+from parcels import FieldSet
 from virtualship.errors import CopernicusCatalogueError
 
 if TYPE_CHECKING:
@@ -619,9 +619,9 @@ def _calc_wp_stationkeeping_time(
     """For a given waypoint (and the instruments present at this waypoint), calculate how much time is required to carry out all instrument deployments."""
     from virtualship.instruments.types import InstrumentType  # avoid circular imports
 
-    assert isinstance(wp_instrument_types, list), (
-        "waypoint instruments must be provided as a list, even if empty."
-    )
+    # to empty list if wp instruments set to 'null'
+    if not wp_instrument_types:
+        wp_instrument_types = []
 
     # TODO: this can be removed if/when CTD and CTD_BGC are merged to a single instrument
     both_ctd_and_bgc = (

From d8141e9dc807a5c836d168d1182aa8bbc787f288 Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Tue, 3 Mar 2026 08:14:03 +0000
Subject: [PATCH 2/4] [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci
---
 src/virtualship/utils.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/virtualship/utils.py b/src/virtualship/utils.py
index 627bd5ec..204e9e8f 100644
--- a/src/virtualship/utils.py
+++ b/src/virtualship/utils.py
@@ -15,8 +15,8 @@
 import numpy as np
 import pyproj
 import xarray as xr
-
 from parcels import FieldSet
+
 from virtualship.errors import CopernicusCatalogueError
 
 if TYPE_CHECKING:

From 62e1bd39e4ba0ae08ff39549b71594db04c1f33c Mon Sep 17 00:00:00 2001
From: j-atkins <106238905+j-atkins@users.noreply.github.com>
Date: Tue, 3 Mar 2026 11:16:46 +0100
Subject: [PATCH 3/4] add test that empty list and null are equivalent and
 return no time

---
 tests/test_utils.py | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/tests/test_utils.py b/tests/test_utils.py
index 00165f27..e68ec19a 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -4,9 +4,9 @@
 import numpy as np
 import pytest
 import xarray as xr
-from parcels import FieldSet
 
 import virtualship.utils
+from parcels import FieldSet
 from virtualship.instruments.types import InstrumentType
 from virtualship.models.expedition import Expedition
 from virtualship.models.location import Location
@@ -347,3 +347,16 @@ class DrifterConfig:
     assert stationkeeping_time_xbt == datetime.timedelta(0), (
         "XBT should have zero stationkeeping time"
     )
+
+
+def test_calc_wp_stationkeeping_time_no_instruments(expedition):
+    """Test calc_wp_stationkeeping_time handles no instruments, either marked as 'null' or empty list."""
+    stationkeeping_emptylist = _calc_wp_stationkeeping_time(
+        [], expedition.instruments_config
+    )
+    stationkeeping_null = _calc_wp_stationkeeping_time(
+        None, expedition.instruments_config
+    )  # "null" in YAML translates to None in Python
+
+    assert stationkeeping_null == stationkeeping_emptylist  # are equivalent
+    assert stationkeeping_null == datetime.timedelta(0)  # at least one is 0 time

From db52ac112361e5a401c0c7ee08c57b6b8fa9f731 Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Tue, 3 Mar 2026 10:18:44 +0000
Subject: [PATCH 4/4] [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci
---
 tests/test_utils.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/test_utils.py b/tests/test_utils.py
index e68ec19a..8f9ec016 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -4,9 +4,9 @@
 import numpy as np
 import pytest
 import xarray as xr
+from parcels import FieldSet
 
 import virtualship.utils
-from parcels import FieldSet
 from virtualship.instruments.types import InstrumentType
 from virtualship.models.expedition import Expedition
 from virtualship.models.location import Location