Fix some missing return type information at maybe.ts file

js/util/maybe.ts

@@ -8,30 +8,30 @@
 export class Maybe<T> {
   private constructor(private value: T | null) {}
 
-  static some<T>(value: T) {
-      if (!value) {
-          throw Error("Provided value must not be empty");
-      }
-      return new Maybe(value);
+  static some<T> (value: T): Maybe<T> {
+    if (!value) {
+      throw Error("Provided value must not be empty");
+    }
+    return new Maybe(value);
   }
 
-  static none<T>() {
-      return new Maybe<T>(null);
+  static none<T> (): Maybe<T> {
+    return new Maybe<T>(null);
   }
 
-  static fromValue<T>(value: T) {
-      return value ? Maybe.some(value) : Maybe.none<T>();
+  static fromValue<T> (value: T): Maybe<T> {
+    return value ? Maybe.some(value) : Maybe.none<T>();
   }
 
-  getOrElse(defaultValue: T) {
-      return this.value === null ? defaultValue : this.value;
+  getOrElse(defaultValue: T): T {
+    return this.value === null ? defaultValue : this.value;
   }
 
   map<R>(f: (wrapped: T) => R): Maybe<R> {
     if (this.value === null) {
-        return Maybe.none<R>();
+      return Maybe.none<R>();
     } else {
-        return Maybe.fromValue(f(this.value));
+      return Maybe.fromValue(f(this.value));
     }
-}
+  }
 }