code: function addExtraFieldsNonDestructive(entry, fields) {
      const exists = propName => fields.find(item => item.field === "property" && item.property === propName);
      const properties = entry.toObject().properties || {};
      return [
          ...fields,
          ...Object.keys(properties)
              .filter(name => !exists(name))
              .map(name =>
                  createFieldDescriptor(
                      entry, // Entry instance
                      name, // Title
                      "property", // Type
                      name, // Property name
                      { removeable: true }
                  )
              )
      ];
  }
docs: Add extra fields to a fields array that are not mentioned in a preset
  Facades are creaded by presets which don't mention all property values (custom user
  added items). This method adds the unmentioned items to the facade fields so that
  they can be edited as well.
  @param {Entry} entry An Entry instance
  @param {Array.<EntryFacadeField>} fields An array of fields
  @returns {Array.<EntryFacadeField>} A new array with all combined fields