feat(compile-core): handle falsy dynamic args for v-on and v-bind (#2393)

fix #2388

packages/shared/src/index.ts

@@ -94,7 +94,8 @@ export const isIntegerKey = (key: unknown) =>
   '' + parseInt(key, 10) === key
 
 export const isReservedProp = /*#__PURE__*/ makeMap(
-  'key,ref,' +
+  // the leading comma is intentional so empty string "" is also included
+  ',key,ref,' +
     'onVnodeBeforeMount,onVnodeMounted,' +
     'onVnodeBeforeUpdate,onVnodeUpdated,' +
     'onVnodeBeforeUnmount,onVnodeUnmounted'
@@ -122,19 +123,22 @@ const hyphenateRE = /\B([A-Z])/g
 /**
  * @private
  */
-export const hyphenate = cacheStringFunction(
-  (str: string): string => {
-    return str.replace(hyphenateRE, '-$1').toLowerCase()
-  }
+export const hyphenate = cacheStringFunction((str: string) =>
+  str.replace(hyphenateRE, '-$1').toLowerCase()
 )
 
 /**
  * @private
  */
 export const capitalize = cacheStringFunction(
-  (str: string): string => {
-    return str.charAt(0).toUpperCase() + str.slice(1)
-  }
+  (str: string) => str.charAt(0).toUpperCase() + str.slice(1)
+)
+
+/**
+ * @private
+ */
+export const toHandlerKey = cacheStringFunction(
+  (str: string) => (str ? `on${capitalize(str)}` : ``)
 )
 
 // compare whether a value has changed, accounting for NaN.