fix(db): Allow string attributes to be null. Never coerce to ""

- Fixes a bug where reply_to_message_id = "" when we receive drafts from the sever.
- In general behavior should be consistent with API. Since they allow null we should too.

spec/models/event-spec.coffee

@@ -79,8 +79,8 @@ describe "Event", ->
   it "accepts a JSON response", ->
     e1 = (new Event).fromJSON(json_event)
     expect(e1.title).toBe "Meeting with Ben Bitdiddle"
-    expect(e1.description).toBe ''
-    expect(e1.location).toBe ''
+    expect(e1.description).toBe null
+    expect(e1.location).toBe null
     expect(e1.start).toBe 1408120200
     expect(e1.end).toBe 1408123800
     expect(e1.participants[0].name).toBe "Ben Bitdiddle"

src/flux/attributes/attribute-string.coffee

@@ -11,7 +11,10 @@ Section: Database
 ###
 class AttributeString extends Attribute
   toJSON: (val) -> val
-  fromJSON: (val) -> val || ""
+  fromJSON: (val) ->
+    return null if val is null or val is undefined or val is false
+    return val + ""
+
 
   # Public: Returns a {Matcher} for objects starting with the provided value.
   startsWith: (val) -> new Matcher(@, 'startsWith', val)

src/flux/tasks/syncback-draft.coffee

@@ -90,12 +90,13 @@ class SyncbackDraftTask extends Task
     if draft.accountId is account.id
       return Promise.resolve(draft)
     else
-      NylasAPI.makeRequest
-        path: "/drafts/#{draft.serverId}"
-        accountId: draft.accountId
-        method: "DELETE"
-        body: {version: draft.version}
-        returnsModel: false
+      if draft.serverId
+        NylasAPI.makeRequest
+          path: "/drafts/#{draft.serverId}"
+          accountId: draft.accountId
+          method: "DELETE"
+          body: {version: draft.version}
+          returnsModel: false
 
       draft.accountId = account.id
       delete draft.serverId