Check that sowdates dictionary really contains an entry for the farm

src/farm/farm.jl

@@ -70,9 +70,15 @@ function stepagent!(farmer::BasicFarmer, model::SimulationModel)
                     @warn "minsowdate and/or maxsowdate is `missing` for crop \"$(ctype.name)\", not assigning sowdates"
                 end
             end
-        elseif cropname(field) == "no growth" && model.date == farmer.sowdates[f]
-            # if a field has been harvested, check if the next crop can be sown
-            @sow(farmer.croprotations[f][1])
+        elseif cropname(field) == "no growth"
+            if haskey(farmer.sowdates, f)
+                if model.date == farmer.sowdates[f]
+                    # if a field has been harvested, check if the next crop can be sown
+                    @sow(farmer.croprotations[f][1])
+                end
+            else
+                @warn "farmer sowdates is empty, farmer = $farmer"
+            end
         end
     end     
 end