made result of first and last methods more strict

Author: transistive

src/Types/CypherList.php

@@ -19,12 +19,14 @@
 use function array_reduce;
 use function array_search;
 use function array_slice;
+use function array_sum;
 use ArrayIterator;
 use BadMethodCallException;
-use function array_sum;
 use function count;
 use function in_array;
+use function is_int;
 use Laudis\Neo4j\Contracts\CypherContainerInterface;
+use OutOfBoundsException;
 use function sort;
 use function usort;
 
@@ -165,11 +167,15 @@ public function find($value)
     }
 
     /**
-     * @return T|null
+     * @return T
      */
     public function first()
     {
-        return $this->array[0] ?? null;
+        if (!isset($this->array[0])) {
+            throw new OutOfBoundsException('Cannot grab first element of an empty list');
+        }
+
+        return $this->array[0];
     }
 
     /**
@@ -192,8 +198,8 @@ public function join(?string $glue = null): string
     public function last()
     {
         $key = array_key_last($this->array);
-        if ($key === null) {
-            return null;
+        if (!is_int($key)) {
+            throw new BadMethodCallException('Cannot grab last element from an empty list');
         }
 
         return $this->array[$key];

src/Types/CypherMap.php

@@ -144,11 +144,11 @@ public function jsonSerialize(): array
     /**
      * @return Pair<string, T>
      */
-    public function first(): ?Pair
+    public function first(): Pair
     {
         $key = array_key_first($this->map);
         if (!is_string($key)) {
-            return null;
+            throw new BadMethodCallException('Cannot grab first element from an empty map');
         }
 
         return new Pair($key, $this->map[$key]);
@@ -157,11 +157,11 @@ public function first(): ?Pair
     /**
      * @return Pair<string, T>
      */
-    public function last(): ?Pair
+    public function last(): Pair
     {
         $key = array_key_last($this->map);
         if (!is_string($key)) {
-            return null;
+            throw new BadMethodCallException('Cannot grab last element from an empty map');
         }
 
         return new Pair($key, $this->map[$key]);