fix PHP 8.1 deprecation warnings (#37087)

Author: jrmajor

src/Illuminate/Collections/Collection.php

@@ -515,10 +515,10 @@ public function implode($value, $glue = null)
         $first = $this->first();
 
         if (is_array($first) || (is_object($first) && ! $first instanceof Stringable)) {
-            return implode($glue, $this->pluck($value)->all());
+            return implode($glue ?? '', $this->pluck($value)->all());
         }
 
-        return implode($value, $this->items);
+        return implode($value ?? '', $this->items);
     }
 
     /**

src/Illuminate/Support/Str.php

@@ -217,7 +217,10 @@ public static function containsAll($haystack, array $needles)
     public static function endsWith($haystack, $needles)
     {
         foreach ((array) $needles as $needle) {
-            if ($needle !== '' && substr($haystack, -strlen($needle)) === (string) $needle) {
+            if (
+                $needle !== '' && $needle !== null
+                && substr($haystack, -strlen($needle)) === (string) $needle
+            ) {
                 return true;
             }
         }

src/Illuminate/Support/Stringable.php

@@ -662,7 +662,7 @@ public function substr($start, $length = null)
      */
     public function substrCount($needle, $offset = null, $length = null)
     {
-        return Str::substrCount($this->value, $needle, $offset, $length);
+        return Str::substrCount($this->value, $needle, $offset ?? 0, $length);
     }
 
     /**