From b793529368c8e3f4bcac4c5267c74889175923ba Mon Sep 17 00:00:00 2001
From: Vecko <36369090+VeckoTheGecko@users.noreply.github.com>
Date: Wed, 18 Jun 2025 15:22:53 +0200
Subject: [PATCH 1/2] Add test_fieldset_time_interval_constant_fields

---
 tests/v4/test_fieldset.py | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/tests/v4/test_fieldset.py b/tests/v4/test_fieldset.py
index 0c39d84953..7e317266bd 100644
--- a/tests/v4/test_fieldset.py
+++ b/tests/v4/test_fieldset.py
@@ -93,6 +93,14 @@ def test_fieldset_time_interval():
     assert fieldset.time_interval.right == np.datetime64("2001-01-01")
 
 
+def test_fieldset_time_interval_constant_fields():
+    fieldset = FieldSet([])
+    fieldset.add_constant_field("constant_field", 1.0)
+    fieldset.add_constant_field("constant_field2", 2.0)
+
+    assert fieldset.time_interval is None
+
+
 def test_fieldset_init_incompatible_calendars():
     ds1 = ds.copy()
     ds1["time"] = xr.date_range("2000", "2001", T_structured, calendar="365_day", use_cftime=True)

From 713e613806585de29b830fdde227931baebb07f0 Mon Sep 17 00:00:00 2001
From: Vecko <36369090+VeckoTheGecko@users.noreply.github.com>
Date: Wed, 18 Jun 2025 14:12:11 +0200
Subject: [PATCH 2/2] Patch time_interval for all constant fields

---
 parcels/fieldset.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/parcels/fieldset.py b/parcels/fieldset.py
index 186698de48..f29526fe3c 100644
--- a/parcels/fieldset.py
+++ b/parcels/fieldset.py
@@ -76,7 +76,9 @@ def time_interval(self):
         time_intervals = (f.time_interval for f in self.fields.values())
 
         # Filter out Nones from constant Fields
-        time_intervals = (t for t in time_intervals if t is not None)
+        time_intervals = [t for t in time_intervals if t is not None]
+        if len(time_intervals) == 0:  # All fields are constant fields
+            return None
         return functools.reduce(lambda x, y: x.intersection(y), time_intervals)
 
     def dimrange(self, dim):