disabled button

http://stackoverflow.com/questions/29941256/validate-polymer-input-on-data-observation

HTML

<link rel="import" href="http://www.polymer-project.org/0.5/components/polymer/polymer.html">
<link rel="import" href="http://www.polymer-project.org/0.5/components/paper-elements/paper-elements.html">
<link rel="import" href="http://www.polymer-project.org/0.5/components/core-elements/core-elements.html">
<body fullbleed layout vertical>
    <form-elem></form-elem>
</body>
<polymer-element name="form-elem" noscript>
    <template>
        <paper-input aria-required="true" floatingLabel label="Id*" value="{{name}}"></paper-input>
        <br>
        <paper-input-decorator floatingLabel label="password">
            <input aria-required="true" id="password" is="core-input" type="password" value="{{password}}" />
        </paper-input-decorator>
        <br>
        <div class="page-holder" horizontal layout center center-justified></div>
        <div class="page-holder" horizontal layout center center-justified>
            <paper-button disabled?="{{!name || !password}}" id="login-button" on-click="{{buttonClick}}">Zaloguj Się</paper-button>
        </div>
    </template>
</polymer-element>