diff --git a/src/appdb.js b/src/appdb.js
index b841962e3..690f25845 100644
--- a/src/appdb.js
+++ b/src/appdb.js
@@ -104,9 +104,6 @@ function postProcess(result) {
         if (envNames[i]) result.env[envNames[i]] = envValues[i];
     }
 
-    // in the db, we store dataDir as unique/nullable
-    result.dataDir = result.dataDir || '';
-
     result.error = safe.JSON.parse(result.errorJson);
     delete result.errorJson;
 
diff --git a/src/apps.js b/src/apps.js
index 73beeae18..77a52bfa2 100644
--- a/src/apps.js
+++ b/src/apps.js
@@ -406,6 +406,8 @@ function getDuplicateErrorDetails(errorMessage, location, domainObject, portBind
 }
 
 function getDataDir(app, dataDir) {
+    assert(dataDir === null || typeof dataDir === 'string');
+
     return dataDir || path.join(paths.APPS_DATA_DIR, app.id, 'data');
 }
 
diff --git a/src/apptask.js b/src/apptask.js
index ba92a065a..c3eea559c 100644
--- a/src/apptask.js
+++ b/src/apptask.js
@@ -442,7 +442,7 @@ function waitForDnsPropagation(app, callback) {
 
 function moveDataDir(app, sourceDir, callback) {
     assert.strictEqual(typeof app, 'object');
-    assert.strictEqual(typeof sourceDir, 'string');
+    assert(sourceDir === null || typeof sourceDir === 'string');
     assert.strictEqual(typeof callback, 'function');
 
     let resolvedSourceDir = apps.getDataDir(app, sourceDir);
@@ -697,12 +697,10 @@ function changeLocation(app, args, progressCallback, callback) {
 
 function migrateDataDir(app, oldDataDir, progressCallback, callback) {
     assert.strictEqual(typeof app, 'object');
-    assert.strictEqual(typeof oldDataDir, 'string');
+    assert(oldDataDir === null || typeof oldDataDir === 'string');
     assert.strictEqual(typeof progressCallback, 'function');
     assert.strictEqual(typeof callback, 'function');
 
-    const dataDirChanged = oldDataDir !== app.dataDir;
-
     async.series([
         progressCallback.bind(null, { percent: 10, message: 'Cleaning up old install' }),
         stopApp.bind(null, app, progressCallback),
@@ -717,6 +715,8 @@ function migrateDataDir(app, oldDataDir, progressCallback, callback) {
 
         // migrate dataDir
         function (next) {
+            const dataDirChanged = oldDataDir !== app.dataDir;
+
             if (!dataDirChanged) return next();
 
             moveDataDir(app, oldDataDir, next);
diff --git a/src/test/database-test.js b/src/test/database-test.js
index 1922b5897..511f0e3c7 100644
--- a/src/test/database-test.js
+++ b/src/test/database-test.js
@@ -412,7 +412,7 @@ describe('database', function () {
             env: {},
             mailboxName: 'talktome',
             enableAutomaticUpdate: true,
-            dataDir: '',
+            dataDir: null,
             tags: [],
             label: null,
             taskId: null
@@ -992,7 +992,7 @@ describe('database', function () {
             },
             mailboxName: 'talktome',
             enableAutomaticUpdate: true,
-            dataDir: '',
+            dataDir: null,
             tags: [],
             label: null,
             taskId: null
@@ -1021,7 +1021,7 @@ describe('database', function () {
             env: {},
             mailboxName: 'callme',
             enableAutomaticUpdate: true,
-            dataDir: '',
+            dataDir: null,
             tags: [],
             label: null,
             taskId: null