Fix for issue #754

During encryption boolean values set to false have
been replaced by nils - that caused the value set to nil in decrypted
domain event.

ruby_event_store/lib/ruby_event_store/mappers/transformation/encryption.rb

@@ -98,7 +98,7 @@ def encrypt_attribute(data, attribute, meta)
           case meta
           when Leaf
             value = data.fetch(attribute)
-            return unless value
+            return if value.nil?
 
             encryption_key = key_repository.key_of(meta.fetch(:identifier))
             encryption_key.encrypt(serializer.dump(value), meta.fetch(:iv))