Update Optionals.

Author: gk-brown

README.md

@@ -1070,7 +1070,7 @@ var set2 = emptySetOf(Integer.class);
 The `Optionals` class contains methods for working with optional (or "nullable") values:
 
 ```java
-public static <T> T coalesce(T value, Supplier<T> supplier) { ... }
+public static <T> T coalesce(T value, Supplier<? extends T> supplier) { ... }
 public static <T, U> U map(T value, Function<? super T, ? extends U> transform) { ... }
 public static <T> void perform(T value, Consumer<? super T> action) { ... }
 ```

kilo-client/src/main/java/org/httprpc/kilo/util/Optionals.java

@@ -42,7 +42,7 @@ private Optionals() {
      * The provided value, or the value produced by the supplier if the value
      * was {@code null}.
      */
-    public static <T> T coalesce(T value, Supplier<T> supplier) {
+    public static <T> T coalesce(T value, Supplier<? extends T> supplier) {
         if (supplier == null) {
             throw new IllegalArgumentException();
         }
@@ -74,7 +74,7 @@ public static <T, U> U map(T value, Function<? super T, ? extends U> transform)
             throw new IllegalArgumentException();
         }
 
-        return (value == null) ? null : transform.apply(value);
+        return (value != null) ? transform.apply(value) : null;
     }
 
     /**