Fix the issue #3

.npmrc

@@ -0,0 +1 @@
+package-lock=false

index.js

@@ -186,9 +186,15 @@ function _setDeep(obj, keyElems, depth, valueCreator) {
   var key = keyElems.shift();
   if (!keyElems.length) {
     var value = valueCreator(obj, key, depth);
-    if (value !== undefined) {
-      obj[key] = value;
+    if (value === undefined) {
+      return;
+    }
+    if (isObject(value)) { // value is always an empty object.
+      if (isObject(obj[key])) {
+        return;
+      }
     }
+    obj[key] = value;
     return;
   }
 

package.json

@@ -11,7 +11,7 @@
     "test": "mocha",
     "coverage": "istanbul cover _mocha",
     "coveralls": "istanbul cover _mocha && istanbul-coveralls",
-    "web:install": "npm i phantomjs-prebuilt mocha-phantomjs",
+    "web:install": "npm install --no-save phantomjs-prebuilt mocha-phantomjs",
     "web:build": "browserify index.js --standalone copyProps | uglifyjs --compress --mangle -o web/copy-props.js && node test/web/make.js",
     "web:test": "mocha-phantomjs -p node_modules/.bin/phantomjs test/web/copy-props.test.html"
   },

test/copy-props-proc.js

@@ -160,6 +160,12 @@ describe('Processing', function() {
       done();
     });
 
+    it('Should do nothing when src prop is an empty object and dst is an ' +
+    'object', function() {
+      var src = { a: { b: {} } };
+      var dst = { a: { b: { c: 1 } } };
+      expect(copyProps(src, dst)).to.deep.equal({ a: { b: { c: 1 } } });
+    });
   });
 
   describe('About fromto special cases', function() {
@@ -249,6 +255,13 @@ describe('Processing', function() {
       done();
     });
 
+    it('Should do nothing when src prop is an empty object and dst is an ' +
+    'object', function() {
+      var src = { a: { b: {} } };
+      var dst = { a: { b: { c: 1 } } };
+      var fromto = ['a.b'];
+      expect(copyProps(src, dst, fromto)).to.deep.equal({ a: { b: { c: 1 } } });
+    });
   });
 
   describe('About patterns of converter returns', function() {

test/web/copy-props-proc.js

@@ -160,6 +160,12 @@ describe('Processing', function() {
       done();
     });
 
+    it('Should do nothing when src prop is an empty object and dst is an ' +
+    'object', function() {
+      var src = { a: { b: {} } };
+      var dst = { a: { b: { c: 1 } } };
+      expect(copyProps(src, dst)).to.deep.equal({ a: { b: { c: 1 } } });
+    });
   });
 
   describe('About fromto special cases', function() {
@@ -249,6 +255,13 @@ describe('Processing', function() {
       done();
     });
 
+    it('Should do nothing when src prop is an empty object and dst is an ' +
+    'object', function() {
+      var src = { a: { b: {} } };
+      var dst = { a: { b: { c: 1 } } };
+      var fromto = ['a.b'];
+      expect(copyProps(src, dst, fromto)).to.deep.equal({ a: { b: { c: 1 } } });
+    });
   });
 
   describe('About patterns of converter returns', function() {