title: How to disable NgbTooltip if tooltip template is empty, in Angular2?
body: <p>I'm showing an array of data inside a tooltip, so I used a template. My code looks like:</p>
  
  <pre><code>&lt;ng-template #ToolTipTemplate&gt;
      &lt;small *ngFor="let month of data.months; let first = first; let last = last"&gt; {{ month.appliedMonthYear | utc | date:'MM/y' }}{{ last ? '' : ', ' }} &lt;/small&gt;
  &lt;/ng-template&gt;
  
  &lt;span [ngbTooltip]="ToolTipTemplate"&gt;Months: {{data.months.length}}&lt;/span&gt;
  </code></pre>
  
  <p>If <code>data.months</code> is empty I do not want the tooltip to appear. Currently if it's empty it shows the tooltip arrow only.</p>
  
  <p>I've tried adding an <code>*ngIf</code> on the <code>&lt;small&gt;</code> tag inside the template, but that didn't work. I've also tried adding <code>*ngIf</code> into <code>&lt;ng-template&gt;</code> to no avail.</p>