diff --git a/dist/recline.dataset.js b/dist/recline.dataset.js
index 4c4b3e38..99fd7876 100644
--- a/dist/recline.dataset.js
+++ b/dist/recline.dataset.js
@@ -733,7 +733,7 @@ this.recline.Backend.Memory = this.recline.Backend.Memory || {};
             var foundmatch = false;
             _.each(self.fields, function(field) {
               var value = rawdoc[field.id];
-              if (value !== null) { 
+              if ((value !== null) && (value !== undefined)) { 
                 value = value.toString();
               } else {
                 // value can be null (apparently in some cases)
diff --git a/dist/recline.js b/dist/recline.js
index 7c8f896a..e1b5f239 100644
--- a/dist/recline.js
+++ b/dist/recline.js
@@ -1038,7 +1038,7 @@ this.recline.Backend.Memory = this.recline.Backend.Memory || {};
             var foundmatch = false;
             _.each(self.fields, function(field) {
               var value = rawdoc[field.id];
-              if (value !== null) { 
+              if ((value !== null) && (value !== undefined)) { 
                 value = value.toString();
               } else {
                 // value can be null (apparently in some cases)
diff --git a/src/backend.memory.js b/src/backend.memory.js
index fd7f6119..c75f6f6f 100644
--- a/src/backend.memory.js
+++ b/src/backend.memory.js
@@ -148,7 +148,7 @@ this.recline.Backend.Memory = this.recline.Backend.Memory || {};
             var foundmatch = false;
             _.each(self.fields, function(field) {
               var value = rawdoc[field.id];
-              if (value !== null) { 
+              if ((value !== null) && (value !== undefined)) { 
                 value = value.toString();
               } else {
                 // value can be null (apparently in some cases)