[fixed] don't alias non existent fields

src/object.js

@@ -178,13 +178,17 @@ inherits(ObjectSchema, MixedSchema, {
 
   from(from, to, alias) {
     return this.transform( obj => {
-      if ( obj == null)
+      var newObj = obj;
+
+      if (obj == null)
         return obj
 
-      var newObj = transform(obj, (o, val, key) => key !== from && (o[key] = val), {})
+      if (has(obj, from)) {
+        newObj = transform(obj, (o, val, key) => key !== from && (o[key] = val), {})
+        newObj[to] = obj[from]
 
-      newObj[to] = obj[from]
-      if(alias) newObj[from] = obj[from]
+        if(alias) newObj[from] = obj[from]
+      }
 
       return newObj
     })
@@ -248,4 +252,4 @@ function sortFields(fields, excludes = []){
   }
 
   return toposort.array(nodes, edges).reverse()
-}
+}

test/object.js

@@ -291,6 +291,19 @@ describe('Object types', function(){
       .should.eql({ myProp: 5, other: 6, Other: 6 })
   })
 
+  it('should not move keys when it does not exist', function(){
+    var inst = object().shape({
+          myProp: mixed(),
+        })
+        .from('prop', 'myProp')
+
+    inst.cast({ myProp: 5 })
+      .should.eql({ myProp: 5 })
+
+    inst.cast({ myProp: 5, prop: 7 })
+      .should.eql({ myProp: 7 })
+  })
+
   it('should handle conditionals', function(){
     var inst = object().shape({
           noteDate: number()
@@ -415,4 +428,4 @@ describe('Object types', function(){
   })
 
 
-})
+})