clutz: Union of two generic functions is Function

[ribrdb]

The following: (reduced from goog.soy.renderAsElement)

/**
 * @param {?function(T, Object<string, *>=):*|?function(T, null=, Object<string, *>=):*} t
 * @param {T=} d 
 * @template T
 */
renderAsElement = function(t, d) {}

becomes function renderAsElement < T > (t : Function | null , d ? : T ) : void
Either function type on its own gets correctly converted. Also if I change the T to string, the union gets correctly converted.