Support for time_interval=None for individual fields

Author: erikvansebille

src/parcels/_core/field.py

@@ -109,6 +109,9 @@ def grid(self):  # TODO PR: Remove in favour of referencing model grid directly
 
     @property
     def time_interval(self):  # TODO PR: Remove in favour of referencing model time_interval directly
+        if "time" not in self.model.data[self.name].dims:
+            # This field does not have a time-dimension
+            return None
         return self.model.time_interval
 
     def __repr__(self):

src/parcels/_core/index_search.py

@@ -77,8 +77,8 @@ def _search_time_index(field: Field, time: np.ndarray):
     if field.time_interval is None:
         return {
             "T": {
-                "index": np.zeros(shape=time.shape, dtype=np.int32),
-                "bcoord": np.zeros(shape=time.shape, dtype=np.float32),
+                "index": np.zeros(shape=np.atleast_1d(time).shape, dtype=np.int32),
+                "bcoord": np.zeros(shape=np.atleast_1d(time).shape, dtype=np.float32),
             }
         }