fix

Author: gengliangwang

sql/catalyst/src/main/scala/org/apache/spark/sql/types/DataType.scala

@@ -448,8 +448,6 @@ object DataType {
 
         fieldCompatible
 
-      case (_: NullType, _) => true
-
       case (w: AtomicType, r: AtomicType) if storeAssignmentPolicy == STRICT =>
         if (!Cast.canUpCast(w, r)) {
           addError(s"Cannot safely cast '$context': $w to $r")
@@ -458,6 +456,8 @@ object DataType {
           true
         }
 
+      case (_: NullType, _) if storeAssignmentPolicy == ANSI => true
+
       case (w: AtomicType, r: AtomicType) if storeAssignmentPolicy == ANSI =>
         if (!Cast.canANSIStoreAssign(w, r)) {
           addError(s"Cannot safely cast '$context': $w to $r")