[dart2js] new-rti: fix merge problem

CQ didn't re-run the tests.

TBR=fishythefish@google.com

Change-Id: I6b8a2d51dc806510f241a95e98e2f1000ef3d79c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/112820
Reviewed-by: Stephen Adams <sra@google.com>

Author: rakudrama

pkg/compiler/lib/src/ssa/optimize.dart

@@ -1359,7 +1359,7 @@ class SsaInstructionSimplifier extends HBaseVisitor
 
     if (_options.experimentNewRti) {
       AbstractValueWithPrecision checkedType =
-          _abstractValueDomain.createFromStaticType(fieldType);
+          _abstractValueDomain.createFromStaticType(fieldType, nullable: true);
       if (checkedType.isPrecise &&
           _abstractValueDomain
               .isIn(value.instructionType, checkedType.abstractValue)