fix: enhance error handling in FillMissingKeys for stateMap conversion

Author: flarco

core/dbio/iop/transforms.go

@@ -830,7 +830,13 @@ func (e *Evaluator) FillMissingKeys(stateMap map[string]any, varsToCheck []strin
 				stateMap[section] = g.M()
 			}
 
-			nested := cast.ToStringMap(stateMap[section])
+			nested, err := cast.ToStringMapE(stateMap[section])
+			if err != nil {
+				g.Warn("could not convert to map to fill missing key for %s: %#v", section, stateMap[section])
+				nested = g.M()
+			} else if nested == nil {
+				nested = g.M()
+			}
 			if _, ok := nested[key]; !ok {
 				nested[key] = nil
 			}