Implementation of the "Black Hole" variant from:
- http://jsperf.com/angularjs-parse-getter/4
- http://jsperf.com/path-evaluation-simplified/7
function cspSafeGetterFn(key0, key1, key2, key3, key4, fullExp) {
  ensureSafeMemberName(key0, fullExp);
  ensureSafeMemberName(key1, fullExp);
  ensureSafeMemberName(key2, fullExp);
  ensureSafeMemberName(key3, fullExp);
  ensureSafeMemberName(key4, fullExp);

  return function cspSafeGetter(scope, locals) {
    var pathVal = (locals && locals.hasOwnProperty(key0)) ? locals : scope;

    if (pathVal == null) return pathVal;
    pathVal = pathVal[key0];

    if (!key1) return pathVal;
    if (pathVal == null) return undefined;
    pathVal = pathVal[key1];

    if (!key2) return pathVal;
    if (pathVal == null) return undefined;
    pathVal = pathVal[key2];

    if (!key3) return pathVal;
    if (pathVal == null) return undefined;
    pathVal = pathVal[key3];

    if (!key4) return pathVal;
    if (pathVal == null) return undefined;
    pathVal = pathVal[key4];

    return pathVal;
  };
}