diff --git a/lib/dao.js b/lib/dao.js
index bd9c81804..68636741c 100644
--- a/lib/dao.js
+++ b/lib/dao.js
@@ -179,10 +179,12 @@ DataAccessObject._forDB = function(data) {
   const res = {};
   for (const propName in data) {
     const type = this.getPropertyType(propName);
-    if (type === 'JSON' || type === 'Any' || type === 'Object' || data[propName] instanceof Array) {
-      res[propName] = JSON.stringify(data[propName]);
+    const value = data[propName];
+    if (value !== null && (type === 'JSON' || type === 'Any' || 
+        type === 'Object' || value instanceof Array)) {
+      res[propName] = JSON.stringify(value);
     } else {
-      res[propName] = data[propName];
+      res[propName] = value;
     }
   }
   return res;
diff --git a/lib/include.js b/lib/include.js
index fab835593..50f2eaa56 100644
--- a/lib/include.js
+++ b/lib/include.js
@@ -903,7 +903,7 @@ Inclusion.include = function(objects, include, options, cb) {
           }
         }
         const targetId = obj[relation.keyFrom];
-        if (targetId) {
+        if (targetId != null) {
           targetIds.push(targetId);
           const targetIdStr = targetId.toString();
           objTargetIdMap[targetIdStr] = objTargetIdMap[targetIdStr] || [];