Apply consistent-return lint rule

lib/versioned-map.js

@@ -19,6 +19,7 @@
 "use strict";
 
 const NONEXISTENT = new Object();
+const UNDEFINED = undefined;
 
 function compareEquality(a, b) {
   var t = typeof a;
@@ -61,14 +62,16 @@ class VersionedMap {
     if (rev == null) rev = this._revision;
 
     var v = this.map.get(key);
-    if (!v) return;
+    if (!v) return UNDEFINED;
 
     for (let i = Math.min(v.length - 1, rev); i >= 0; --i) {
       if (i in v) {
-        if (v[i] === NONEXISTENT) return undefined;
+        if (v[i] === NONEXISTENT) return UNDEFINED;
         else return v[i];
       }
     }
+
+    return UNDEFINED;
   }
 
   has(key, rev) {
@@ -99,7 +102,7 @@ class VersionedMap {
       v = [];
       v[rev] = value;
       this.map.set(key, v);
-      return this;
+      return;
     }
 
     var old = v[Math.min(rev, v.length - 1)];