Merge pull request #15992 from garyo/fix/gltf-export-avoid-null

GLTFExporter: omit null indices

examples/js/exporters/GLTFExporter.js

@@ -1360,6 +1360,8 @@ THREE.GLTFExporter.prototype = {
 
 					}
 
+					if ( primitive.indices === null ) delete primitive.indices;
+
 				}
 
 				var material = processMaterial( materials[ groups[ i ].materialIndex ] );