Angular Schematics: trustedSubscriber._addParentTeardownLogic

I'm trying to build an Angular Schematics to help me and my team create NgRx actions fast. This is the schematics function, most of it is copied from various tutorials:

export default (options: CCSchematicsAction): Rule => {
    return (tree: Tree, _context: SchematicContext) => {
        const modulePath = options.modulePath.replace(/-?module$/, ""); // "shared/application-tools"
        const moduleFolder = normalize("src/app/" + modulePath); // "src/app/shared/application-tools"
        const modulePathComponents = modulePath.split("/"); // ["shared", "application-tools"]
        const moduleIdentifier = modulePathComponents
            .map(part => classify(part))
            .join(".")
        + ".Action"; // "Shared.ApplicationTools.Action"

        const action = options.name.replace(/-?action$/, "");
        const path = normalize(moduleFolder + "/action/" + action) + "/";

        const templateSource = apply(url("./files"), [
            template({
                action: action,
                moduleIdentifier: moduleIdentifier
            }),
            move(path)
        ]);

        return chain([
            mergeWith(templateSource)
        ])(tree, _context);
    };
}

I invoke the schematics with

schematics cc-generate:action load-stuff-action --modulePath shared/ui

and get the following, which I can't even find any info to on the web:

TypeError: trustedSubscriber._addParentTeardownLogic is not a function
    at MergeMapSubscriber.Subscriber [as constructor] (/Users/voss/Development/cc/cc-schematics/node_modules/rxjs/internal/Subscriber.js:45:43)
    at MergeMapSubscriber.OuterSubscriber [as constructor] (/Users/voss/Development/cc/cc-schematics/node_modules/rxjs/internal/OuterSubscriber.js:20:42)
    at new MergeMapSubscriber (/Users/voss/Development/cc/cc-schematics/node_modules/rxjs/internal/operators/mergeMap.js:48:28)
    at MergeMapOperator.call (/Users/voss/Development/cc/cc-schematics/node_modules/rxjs/internal/operators/mergeMap.js:39:33)
    at Observable.subscribe (/Users/voss/Development/cc/cc-schematics/node_modules/rxjs/internal/Observable.js:24:22)
    at DefaultIfEmptyOperator.call (/usr/local/lib/node_modules/@angular-devkit/schematics-cli/node_modules/rxjs/internal/operators/defaultIfEmpty.js:24:23)
    at Observable.subscribe (/Users/voss/Development/cc/cc-schematics/node_modules/rxjs/internal/Observable.js:24:22)
    at TakeLastOperator.call (/usr/local/lib/node_modules/@angular-devkit/schematics-cli/node_modules/rxjs/internal/operators/takeLast.js:35:23)
    at Observable.subscribe (/Users/voss/Development/cc/cc-schematics/node_modules/rxjs/internal/Observable.js:24:22)
    at DoOperator.call (/usr/local/lib/node_modules/@angular-devkit/schematics-cli/node_modules/rxjs/internal/operators/tap.js:29:23)

Edit:

When I remove everything and just return an empty chain, the error stays.

export default (_options: CCSchematicsAction): Rule => {
    return (tree: Tree, _context: SchematicContext) => {
        return chain([noop()])(tree, _context);
    };
}

So what's wrong with the chain function?