Don't crash on explicit boxing casts

e.g.: `static final boolean Z = (Boolean) true;` is well-formed, but not
a constant expression.

MOE_MIGRATED_REVID=215487485

1 files changed, 2 insertions, 1 deletions

diff --git a/java/com/google/turbine/binder/ConstEvaluator.java b/java/com/google/turbine/binder/ConstEvaluator.java
index 8c8257e..450c686 100644
--- a/java/com/google/turbine/binder/ConstEvaluator.java
+++ b/java/com/google/turbine/binder/ConstEvaluator.java
@@ -444,7 +444,8 @@ public strictfp class ConstEvaluator {
           ClassTy classTy = (ClassTy) t.ty();
           // TODO(cushon): check package?
           if (!classTy.name().equals("String")) {
-            throw new AssertionError(classTy);
+            // Explicit boxing cases (e.g. `(Boolean) false`) are legal, but not const exprs.
+            return null;
           }
           return expr.asString();
         }