fix: for tag not respecting Drop#valueOf(), fixes #515

src/drop/drop.ts

@@ -1,8 +1,4 @@
 export abstract class Drop {
-  public valueOf (): any {
-    return undefined
-  }
-
   public liquidMethodMissing (key: string | number): Promise<string | undefined> | string | undefined {
     return undefined
   }

src/util/collection.ts

@@ -1,6 +1,7 @@
-import { isNil, isString, isObject, isArray, isIterable } from './underscore'
+import { isNil, isString, isObject, isArray, isIterable, toValue } from './underscore'
 
 export function toEnumerable (val: any) {
+  val = toValue(val)
   if (isArray(val)) return val
   if (isString(val) && val.length > 0) return [val]
   if (isIterable(val)) return Array.from(val)

src/util/underscore.ts

@@ -39,7 +39,7 @@ export function stringify (value: any): string {
 }
 
 export function toValue (value: any): any {
-  return value instanceof Drop ? value.valueOf() : value
+  return (value instanceof Drop && isFunction(value.valueOf)) ? value.valueOf() : value
 }
 
 export function isNumber (value: any): value is number {