Reverting that key in eval can be a ParticleSet

As suggested in #2122 (comment)

Author: erikvansebille

parcels/field.py

@@ -18,7 +18,6 @@
 )
 from parcels.application_kernels.interpolation import UXPiecewiseLinearNode, XLinear, ZeroInterpolator
 from parcels.particle import KernelParticle
-from parcels.particleset import ParticleSet
 from parcels.tools.converters import (
     UnitConverter,
     unitconverters_map,
@@ -36,9 +35,9 @@
 
 
 def _deal_with_errors(error, key, vector_type: VectorType):
-    if isinstance(key, (ParticleSet, KernelParticle)):
+    if isinstance(key, KernelParticle):
         key.state = AllParcelsErrorCodes[type(error)]
-    elif isinstance(key[-1], (ParticleSet, KernelParticle)):
+    elif isinstance(key[-1], KernelParticle):
         key[-1].state = AllParcelsErrorCodes[type(error)]
     else:
         raise RuntimeError(f"{error}. Error could not be handled because particle was not part of the Field Sampling.")
@@ -256,7 +255,7 @@ def eval(self, time: datetime, z, y, x, particle=None, applyConversion=True):
     def __getitem__(self, key):
         self._check_velocitysampling()
         try:
-            if isinstance(key, (KernelParticle, ParticleSet)):
+            if isinstance(key, KernelParticle):
                 return self.eval(key.time, key.depth, key.lat, key.lon, key)
             else:
                 return self.eval(*key)
@@ -348,7 +347,7 @@ def eval(self, time: datetime, z, y, x, particle=None, applyConversion=True):
 
     def __getitem__(self, key):
         try:
-            if isinstance(key, (KernelParticle, ParticleSet)):
+            if isinstance(key, KernelParticle):
                 return self.eval(key.time, key.depth, key.lat, key.lon, key)
             else:
                 return self.eval(*key)