It’s best to check if geometry.index is null. If so, using Blender or a similar tool is the easiest solution.
No, since Geometry does have a method .mergeVertices(). I think sooner or later BufferGeometry needs a similar functionality. For now try this:
var tempGeometry = new THREE.Geometry().fromBufferGeometry( geometry );
tempGeometry.mergeVertices();
tempGeometry.computeVertexNormals();
geometry = new THREE.BufferGeometry().fromGeometry( tempGeometry );