code: function resolveBoolOrFunc(a, params, defaultValue) {
            var item = params.item;
            var $scope = params.$scope;
            var event = params.event;
            var modelValue = params.modelValue;
  
            defaultValue = isBoolean(defaultValue) ? defaultValue : true;
  
            if (isBoolean(a)) {
              return a;
            } else if (angular.isFunction(a)) {
              return a.call($scope, $scope, event, modelValue);
            } else {
              return defaultValue;
            }
          }
docs: Resolves a boolean or a function that returns a boolean
  Returns true by default if the param is null or undefined
  @param a - the parameter to be checked
  @param params - the object for the item's parameters
  @param defaultValue - the default boolean value to use if the parameter is
  neither a boolean nor function. True by default.