Merge pull request #80 from boesing/qa/hardening-type-safety

qa: hardening type-safety for `JsonSerializable` implementation

Author: boesing

src/Map.php

@@ -384,7 +384,7 @@ public function slice(int $length): MapInterface
 
     public function jsonSerialize(): ?array
     {
-        if ($this->isEmpty()) {
+        if ($this->data === []) {
             return null;
         }
 

src/MapInterface.php

@@ -183,4 +183,9 @@ public function join(string $separator = ''): string;
      * @throws RuntimeException if a new key is being generated more than once.
      */
     public function keyExchange(callable $keyGenerator): MapInterface;
+
+    /**
+     * @psalm-return non-empty-array<TKey,TValue>|null
+     */
+    public function jsonSerialize(): ?array;
 }

src/OrderedListInterface.php

@@ -150,4 +150,9 @@ public function join(string $separator = ''): string;
      * @psalm-return list<TValue>
      */
     public function toNativeArray(): array;
+
+    /**
+     * @psalm-return list<TValue>
+     */
+    public function jsonSerialize(): array;
 }