Index: oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/Collision.java
===================================================================
--- oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/Collision.java	(revision 1594908)
+++ oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/Collision.java	(working copy)
@@ -127,7 +127,7 @@
         if (commitRoot.isCommitted(revision)) {
             return false;
         }
-        op.setMapEntry(NodeDocument.COLLISIONS, revision, true);
+        op.setMapEntry(NodeDocument.COLLISIONS, revision, String.valueOf(true));
         commitRoot = store.createOrUpdate(Collection.NODES, op);
         // check again on old document right before our update was applied
         if (commitRoot.isCommitted(revision)) {
Index: oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/UpdateOp.java
===================================================================
--- oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/UpdateOp.java	(revision 1594908)
+++ oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/UpdateOp.java	(working copy)
@@ -130,7 +130,7 @@
      * @param revision the revision
      * @param value the value
      */
-    void setMapEntry(@Nonnull String property, @Nonnull Revision revision, Object value) {
+    void setMapEntry(@Nonnull String property, @Nonnull Revision revision, String value) {
         Operation op = new Operation();
         op.type = Operation.Type.SET_MAP_ENTRY;
         op.value = value;