Ensure _.assign, _.extend, _.defaults, and _.merge coerce values to objects.

lodash.src.js

@@ -2989,6 +2989,7 @@
           customizer = length < 3 ? undefined : customizer;
           length = 1;
         }
+        object = toObject(object);
         while (++index < length) {
           var source = sources[index];
           if (source) {
@@ -4017,7 +4018,12 @@
      * @returns {*} Returns the value to assign to the destination object.
      */
     function mergeDefaults(objectValue, sourceValue) {
-      return objectValue === undefined ? sourceValue : merge(objectValue, sourceValue, mergeDefaults);
+      if (objectValue === undefined) {
+        return sourceValue;
+      }
+      return isObject(objectValue)
+        ? merge(objectValue, sourceValue, mergeDefaults)
+        : objectValue;
     }
 
     /**
@@ -8575,9 +8581,6 @@
      * // => { 'fruits': ['apple', 'banana'], 'vegetables': ['beet', 'carrot'] }
      */
     var merge = createAssigner(function baseMerge(object, source, customizer, stackA, stackB) {
-      if (!isObject(object)) {
-        return object;
-      }
       var isSrcArr = isArrayLike(source) && (isArray(source) || isTypedArray(source)),
           props = isSrcArr ? undefined : keysIn(source);
 
@@ -8639,9 +8642,11 @@
      */
     var assign = createAssigner(function(object, source, customizer) {
       var props = keys(source);
-      return customizer
-        ? copyObjectWith(source, props, customizer, object)
-        : copyObject(source, props, object)
+      if (customizer) {
+        copyObjectWith(source, props, customizer, object);
+      } else {
+        copyObject(source, props, object);
+      }
     });
 
     /**
@@ -8705,11 +8710,7 @@
      * // => { 'user': 'barney', 'age': 36 }
      */
     var defaults = restParam(function(args) {
-      var object = args[0];
-      if (object == null) {
-        return object;
-      }
-      args.push(extendDefaults);
+      args.push(undefined, extendDefaults);
       return extend.apply(undefined, args);
     });
 
@@ -8732,11 +8733,7 @@
      *
      */
     var defaultsDeep = restParam(function(args) {
-      var object = args[0];
-      if (object == null) {
-        return object;
-      }
-      args.push(mergeDefaults);
+      args.push(undefined, mergeDefaults);
       return merge.apply(undefined, args);
     });
 
@@ -8758,9 +8755,11 @@
      */
     var extend = createAssigner(function(object, source, customizer) {
       var props = keysIn(source);
-      return customizer
-        ? copyObjectWith(source, props, customizer, object)
-        : copyObject(source, props, object)
+      if (customizer) {
+        copyObjectWith(source, props, customizer, object);
+      } else {
+        copyObject(source, props, object);
+      }
     });
 
     /**

test/test.js

@@ -5058,12 +5058,15 @@
         isAssign = methodName == 'assign',
         isDefaults = methodName == 'defaults';
 
-    test('`_.' + methodName + '` should pass thru falsey `object` values', 1, function() {
+    test('`_.' + methodName + '` should coerce primitives to objects', 1, function() {
+      var expected = _.map(falsey, _.constant(true));
+
       var actual = _.map(falsey, function(object, index) {
-        return index ? func(object) : func();
+        var result = index ? func(object) : func();
+        return _.isEqual(result, Object(object));
       });
 
-      deepEqual(actual, falsey);
+      deepEqual(actual, expected);
     });
 
     test('`_.' + methodName + '` should assign own ' + (isAssign ? '' : 'and inherited ') + 'source properties', 1, function() {
@@ -5122,7 +5125,7 @@
 
       var actual = _.map([null, undefined], function(value) {
         try {
-          return _.isEqual(func(value, { 'a': 1 }), value);
+          return _.isEqual(func(value, { 'a': 1 }), {});
         } catch(e) {
           return false;
         }
@@ -11667,7 +11670,7 @@
           expected = { 'a': { 'b': 1, 'c': 3 } };
 
       var defaultsDeep = _.partialRight(_.merge, function deep(value, other) {
-        return _.merge(value, other, deep);
+        return _.isObject(value) ? _.merge(value, other, deep) : value;
       });
 
       deepEqual(defaultsDeep(object, source), expected);