Fix the typing of ijdata. It's supposed to either be undefined or not null as seen in  javascript/template/soy/templates.ts
@@ -486,7 +486,7 @@ public final class JsType {
parameters.isEmpty()
? "null"
: "{" + Joiner.on(", ").withKeyValueSeparator(": ").join(parameters) + ",}";
- String ijType = "?goog.soy.IjData";
+ String ijType = "(goog.soy.IjData|undefined)";
String returnType = forReturnType.typeExpr();
if (kind == JsTypeKind.IDOMSRC) {
builder.addRequire(
