src/jdk.scripting.nashorn/share/classes/jdk/nashorn/internal/codegen/MapCreator.java

*** 98,116 ****
          assert tuples != null;
  
          for (final MapTuple<T> tuple : tuples) {
              final String key    = tuple.key;
              final Symbol symbol = tuple.symbol;
  
              //TODO initial type is object here no matter what. Is that right?
              if (symbol != null && !isValidArrayIndex(getArrayIndex(key))) {
                  final int flags = getPropertyFlags(symbol, hasArguments, false);
                  properties.add(
                          new SpillProperty(
                                  key,
                                  flags,
!                                 spillIndex++));
              }
          }
  
          return PropertyMap.newMap(properties, structure.getName(), 0, 0, spillIndex);
      }
--- 98,118 ----
          assert tuples != null;
  
          for (final MapTuple<T> tuple : tuples) {
              final String key    = tuple.key;
              final Symbol symbol = tuple.symbol;
+             final Class<?> initialType = tuple.getValueType();
  
              //TODO initial type is object here no matter what. Is that right?
              if (symbol != null && !isValidArrayIndex(getArrayIndex(key))) {
                  final int flags = getPropertyFlags(symbol, hasArguments, false);
                  properties.add(
                          new SpillProperty(
                                  key,
                                  flags,
!                                 spillIndex++,
!                                 initialType));
              }
          }
  
          return PropertyMap.newMap(properties, structure.getName(), 0, 0, spillIndex);
      }