packages/optimizely-sdk/lib/core/custom_attribute_condition_evaluator/index.js
function existsEvaluator(condition, userAttributes) {
  var userValue = userAttributes[condition.name];
  return typeof userValue !== 'undefined' && userValue !== null;
}
function existsEvaluator(condition, userAttributes) {
  var userValue = userAttributes[condition.name];
  return typeof userValue !== 'undefined' && userValue !== null;
}
function existsEvaluator ( condition , userAttributes ) { var userValue = userAttributes [ condition . name ] ; return typeof userValue !== 'undefined' && userValue !== null ; }
Evaluate the given exists match condition for the given user attributes
@param   {Object}  condition
@param   {Object}  userAttributes
@returns {Boolean} true if both:
1) the user attributes have a value for the given condition, and
2) the user attribute value is neither null nor undefined
Returns false otherwise
Evaluate the given exists match condition for the given user attributes