Polymer 3 build yields 0-byte my-app.js - polymer

Question

I seem to have encountered a problem similar to this.
file my-app.js:
import {PolymerElement, html} from "../node_modules/#polymer/polymer/polymer-element.js";
import "../node_modules/#polymer/polymer/lib/elements/dom-if.js";
import "../node_modules/#polymer/app-route/app-location.js";
import "../node_modules/#polymer/app-route/app-route.js";
class MyApp extends PolymerElement {
...
}
customElements.define('my-app',MyApp);
file polymer.json:
{
"entrypoint":"index.html"
,"shell":"src/my-app.js"
,"builds":[
{
"preset":"es5-bundled"
,"addServiceWorker": false
}
]
}
command polymer build produces file my-app.js with 0 byte. All other built files look correct according to my naked eyes (at least they are not truncated to 0 byte).
I then re-built the application with the following "dev" polymer.json:
"builds":[
{
"name": "dev",
"addServiceWorker": false,
"js": {"minify": false, "compile": false},
"css": {"minify": false},
"html": {"minify": false},
"bundle": false,
"addPushManifest": false
}
]
The built my-app.js looks correct with this "dev" configuration. However, browser's sources window highlights with red under score the first of the followings lines:
import {PolymerElement, html} from "../node_modules/#polymer/polymer/polymer-element.js";
import "../node_modules/#polymer/polymer/lib/elements/dom-if.js";
import "../node_modules/#polymer/app-route/app-location.js";
import "../node_modules/#polymer/app-route/app-route.js";
and console window prints this strange message:
Uncaught TypeError: Failed to resolve module specifier "#polymer/polymer/polymer-legacy.js". Relative references must start with either "/", "./", or "../". (index):1
I have searched all my .js files and directory ../node_modules/ and have not found any file containing polymer-legacy.js.
Helps will be much appreciated.
EDIT
Thank you for the attention!
These weird symptoms are caused by the stale polymer 1.6.0 which was installed in /usr/local/bin/polymer using yarn .
These issues are gone with polymer 1.7.2.