deepMixIn causes valid properties to be merged by 'undefined` values in onConflict="merge" strategy

[zeesulehria]

Description

If I have a record in cache with valid properites, and later on if its gets 'merged with another version of this record that has some of the properties 'undefined, valid properties present in cache earlier gets over-written with 'undefined' values in deepMixIn() function.

Here is current implementation of this function:

deepMixIn: function deepMixIn(dest, source) {
      if (source) {
        for (var key in source) {
          var value = source[key];
          var existing = dest[key];
          if (isPlainObject(value) && isPlainObject(existing)) {
            utils.deepMixIn(existing, value);
          } else  {
            dest[key] = value;
          }
        }
      }
      return dest;
    },

And we can fix it by changing it like:

deepMixIn: function deepMixIn(dest, source) {
      if (source) {
        for (var key in source) {
          var value = source[key];
          var existing = dest[key];
          if (isPlainObject(value) && isPlainObject(existing)) {
            utils.deepMixIn(existing, value);
          } else if (typeof value !== 'undefined') {
            dest[key] = value;
          }
        }
      }
      return dest;
    },

Environment

• js-data version:
  "js-data": "^3.0.5",
  "js-data-http": "^3.0.1",
• node or browser version: v10.7.0
• operating system: macOS

Thanks!