fixes #54

Signed-off-by: Mohamad Ahmadi <mohamadhasan.ahmadi@gmail.com>

src/color-thief.js

@@ -128,7 +128,7 @@ ColorThief.prototype.getPalette = function(sourceImage, colorCount, quality) {
     // Send array to quantize function which clusters values
     // using median cut algorithm
     var cmap    = MMCQ.quantize(pixelArray, colorCount);
-    var palette = cmap.palette();
+    var palette = cmap? cmap.palette() : null;
 
     // Clean up
     image.removeCanvas();