<svg xmlns="http://www.w3.org/2000/svg">
  <defs>
    <path id="path" d="" />
  </defs>

  <rect fill="lime" width="100%" height="100%"/>

  <text y="50" font-size="50" fill="red" >
    <textPath path="">Empty paths should be invisible</textPath>
  </text>

  <text y="100" font-size="50" fill="red" >
    <textPath href="#path">Empty paths should be invisible</textPath>
  </text>

  <text y="150" font-size="50" fill="red" >
    <textPath>No path at all should be invisible too</textPath>
  </text>
</svg>