diff --git a/src/Illuminate/Database/Eloquent/Builder.php b/src/Illuminate/Database/Eloquent/Builder.php
index 2d0ec3ec37fe..24ab0e4e95ab 100755
--- a/src/Illuminate/Database/Eloquent/Builder.php
+++ b/src/Illuminate/Database/Eloquent/Builder.php
@@ -193,7 +193,7 @@ public function whereKey($id)
             return $this;
         }
 
-        if ($this->model->getKeyType() === 'string') {
+        if ($id !== null && $this->model->getKeyType() === 'string') {
             $id = (string) $id;
         }
 
@@ -214,7 +214,7 @@ public function whereKeyNot($id)
             return $this;
         }
 
-        if ($this->model->getKeyType() === 'string') {
+        if ($id !== null && $this->model->getKeyType() === 'string') {
             $id = (string) $id;
         }
 
diff --git a/src/Illuminate/Foundation/Application.php b/src/Illuminate/Foundation/Application.php
index 3ef3a2eb4818..28109474e5c9 100755
--- a/src/Illuminate/Foundation/Application.php
+++ b/src/Illuminate/Foundation/Application.php
@@ -33,7 +33,7 @@ class Application extends Container implements ApplicationContract, CachesConfig
      *
      * @var string
      */
-    const VERSION = '7.26.0';
+    const VERSION = '7.26.1';
 
     /**
      * The base path for the Laravel installation.
diff --git a/tests/Database/DatabaseEloquentBuilderTest.php b/tests/Database/DatabaseEloquentBuilderTest.php
index cbccc88ba216..07b3ff8185e9 100755
--- a/tests/Database/DatabaseEloquentBuilderTest.php
+++ b/tests/Database/DatabaseEloquentBuilderTest.php
@@ -1063,6 +1063,19 @@ public function testWhereKeyMethodWithStringZero()
         $builder->whereKey($int);
     }
 
+    public function testWhereKeyMethodWithStringNull()
+    {
+        $model = new EloquentBuilderTestStubStringPrimaryKey();
+        $builder = $this->getBuilder()->setModel($model);
+        $keyName = $model->getQualifiedKeyName();
+
+        $builder->getQuery()->shouldReceive('where')->once()->with($keyName, '=', m::on(function ($argument) {
+            return $argument === null;
+        }));
+
+        $builder->whereKey(null);
+    }
+
     public function testWhereKeyMethodWithArray()
     {
         $model = $this->getMockModel();
@@ -1102,6 +1115,19 @@ public function testWhereKeyNotMethodWithStringZero()
         $builder->whereKeyNot($int);
     }
 
+    public function testWhereKeyNotMethodWithStringNull()
+    {
+        $model = new EloquentBuilderTestStubStringPrimaryKey();
+        $builder = $this->getBuilder()->setModel($model);
+        $keyName = $model->getQualifiedKeyName();
+
+        $builder->getQuery()->shouldReceive('where')->once()->with($keyName, '!=', m::on(function ($argument) {
+            return $argument === null;
+        }));
+
+        $builder->whereKeyNot(null);
+    }
+
     public function testWhereKeyNotMethodWithInt()
     {
         $model = $this->getMockModel();