Update MD004/ul-style to handle invalid "style" parameter values.

demo/markdownlint-browser.js

@@ -1849,6 +1849,7 @@ var differentItemStyle = {
     "plus": "asterisk",
     "asterisk": "dash"
 };
+var validStyles = Object.keys(expectedStyleToMarker);
 module.exports = {
     "names": ["MD004", "ul-style"],
     "description": "Unordered list style",
@@ -1874,6 +1875,9 @@ module.exports = {
                         }
                         expectedStyle = nestingStyles[nesting];
                     }
+                    if (!validStyles.includes(expectedStyle)) {
+                        expectedStyle = validStyles[0];
+                    }
                     var range = null;
                     var fixInfo = null;
                     var match = item.line.match(listItemMarkerRe);

lib/md004.js

@@ -11,12 +11,12 @@ const expectedStyleToMarker = {
   "plus": "+",
   "asterisk": "*"
 };
-
 const differentItemStyle = {
   "dash": "plus",
   "plus": "asterisk",
   "asterisk": "dash"
 };
+const validStyles = Object.keys(expectedStyleToMarker);
 
 module.exports = {
   "names": [ "MD004", "ul-style" ],
@@ -43,6 +43,9 @@ module.exports = {
             }
             expectedStyle = nestingStyles[nesting];
           }
+          if (!validStyles.includes(expectedStyle)) {
+            expectedStyle = validStyles[0];
+          }
           let range = null;
           let fixInfo = null;
           const match = item.line.match(listItemMarkerRe);

test/invalid-ul-style-style.md

@@ -0,0 +1,16 @@
+# Invalid ul-style style
+
+* Item {MD004}
+  * Item {MD004}
+
++ Item {MD004}
+  + Item {MD004}
+
+- Item
+  - Item
+
+<!-- markdownlint-configure-file {
+  "ul-style": {
+    "style": "invalid"
+  }
+} -->