Material: Fixed toJSON() as root. See #7337

src/materials/Material.js

@@ -115,6 +115,17 @@ THREE.Material.prototype = {
 
 	toJSON: function ( meta ) {
 
+		var isRoot = meta === undefined;
+
+		if ( isRoot ) {
+
+			meta = {
+				textures: {},
+				images: {}
+			};
+
+		}
+
 		var data = {
 			metadata: {
 				version: 4.4,
@@ -176,6 +187,28 @@ THREE.Material.prototype = {
 		if ( this.alphaTest > 0 ) data.alphaTest = this.alphaTest;
 		if ( this.wireframe === true ) data.wireframe = this.wireframe;
 		if ( this.wireframeLinewidth > 1 ) data.wireframeLinewidth = this.wireframeLinewidth;
+	
+		// TODO: Copied from Object3D.toJSON
+
+		function extractFromCache ( cache ) {
+			var values = [];
+			for ( var key in cache ) {
+				var data = cache[ key ];
+				delete data.metadata;
+				values.push( data );
+			}
+			return values;
+		}
+
+		if ( isRoot ) {
+
+			var textures = extractFromCache( meta.textures );
+			var images = extractFromCache( meta.images );
+
+			if ( textures.length > 0 ) data.textures = textures;
+			if ( images.length > 0 ) data.images = images;
+
+		}
 
 		return data;