code: function getOrDefault ( source, path, defaultVal ) {
      var isAlreadySplitted = isArray( path );
  
      if ( !isDefined(source) ) return defaultVal;
      if ( !isString(path) && !isAlreadySplitted ) return defaultVal;
  
      var tokens = isAlreadySplitted ? path : path.split( '.' )
        , idx, key;
  
      for ( idx in tokens ) {
          key = tokens[ idx ];
  
          if ( isDefined( source[key] ) ) 
              source = source[ key ];
          else 
              return defaultVal;
      }
  
      return source;
  }
docs: Returns path's value or null if path's chain has undefined member.
  @param {Object} source - root object.
  @param {string} path - path to `source` value.
  @return {Object}