fix memory leak issue with CGMutablePathRef

lib/extract/extractStroke.js

@@ -1,5 +1,6 @@
 import extractBrush from './extractBrush';
 import extractOpacity from './extractOpacity';
+import _ from 'lodash';
 let separator = /\s*,\s*/;
 
 const caps = {
@@ -15,12 +16,19 @@ const joins = {
 };
 
 export default function(props) {
-    let strokeWidth = +props.strokeWidth;
     let {stroke} = props;
-    if (!strokeWidth && !stroke) {
+    if (!stroke) {
         return null;
     }
 
+    let strokeWidth = +props.strokeWidth;
+
+    if (_.isNil(props.strokeWidth)) {
+        strokeWidth = 1;
+    } else if (!strokeWidth) {
+        return;
+    }
+
     let strokeDasharray = props.strokeDasharray;
 
     if (typeof strokeDasharray === 'string') {
@@ -42,7 +50,7 @@ export default function(props) {
         strokeLinecap: caps[props.strokeLinecap] || 0,
         strokeLinejoin: joins[props.strokeLinejoin] || 0,
         strokeDasharray: strokeDasharray || null,
-        strokeWidth: strokeWidth || 1,
+        strokeWidth: strokeWidth,
         strokeDashoffset: strokeDasharray ? (+props.strokeDashoffset || 0) : null,
         strokeMiterlimit: props.strokeMiterlimit || 4
     };