incorporated suggestions from @katzyn

h2/src/main/org/h2/mvstore/db/MVSecondaryIndex.java

@@ -267,7 +267,7 @@ public final class MVSecondaryIndex extends BaseIndex implements MVIndex {
         return new MVStoreCursor(session, map.keyIterator(min, max, false));
     }
 
-    private ValueArray convertToKey(ValueArray r, Boolean minmax) {
+    private static ValueArray convertToKey(ValueArray r, Boolean minmax) {
         if (r == null) {
             return null;
         }

h2/src/main/org/h2/mvstore/db/ValueDataType.java

@@ -158,9 +158,15 @@ public class ValueDataType implements DataType {
         }
 
         int t2 = Value.getHigherOrder(a.getType(), b.getType());
+        if (t2 == Value.ENUM) {
             String[] enumerators = ValueEnum.getEnumeratorsForBinaryOperation(a, b);
-        int comp = a.convertTo(t2, -1, mode, null, enumerators)
-                .compareTypeSafe(b.convertTo(t2, -1, mode, null, enumerators), compareMode);
+            a = a.convertToEnum(enumerators);
+            b = b.convertToEnum(enumerators);
+        } else {
+            a = a.convertTo(t2, -1, mode);
+            b = b.convertTo(t2, -1, mode);
+        }
+        int comp = a.compareTypeSafe(b, compareMode);
 
         if ((sortType & SortOrder.DESCENDING) != 0) {
             comp = -comp;