Palette::findMaxPopulation() returns null for no swatches

Author: yarri

src/Palette.php

@@ -76,6 +76,9 @@ public function __construct($swatches)
 
     private function findMaxPopulation()
     {
+        if (!$this->swatches) {
+            return null;
+        }
         return max(array_map(function (Swatch $swatch) {
             return $swatch->getPopulation();
         }, $this->swatches));