fix: FlatMapAuto uses NonNullable<T> (#142)

Author: patrickmichalina

src/maybe/maybe.interface.ts

@@ -96,7 +96,7 @@ export interface IMaybe<T> extends IMonad<T> {
   /**
    * Combine multiple Maybe, automatically wrapping predicate
    */
-  flatMapAuto<R>(fn: (v: T) => R): IMaybe<NonNullable<R>>
+  flatMapAuto<R>(fn: (v: NonNullable<T>) => R): IMaybe<NonNullable<R>>
 
   /**
    * Apply a predicate which if met, continues the Maybe chain,

src/maybe/maybe.spec.ts

@@ -456,6 +456,17 @@ describe('Maybe', () => {
 
       expect(maybeAString).toBeUndefined()
     })
+
+    it('should be nonnullable value outlet', () => {
+      const imgWidth = maybe('url.com')
+        .flatMapAuto(imgUrl => /width=[0-9]*/.exec(imgUrl))
+        .flatMapAuto(a => a[0].split('=')[1])
+        .map(a => +a)
+        .valueOr(0)
+
+      expect(imgWidth).toEqual(0)
+    })
+
   })
 
   describe('isSome', () => {