Addtional unit tests for vlue binders

src/PhpSpreadsheet/Cell/DefaultValueBinder.php

@@ -26,6 +26,7 @@ class DefaultValueBinder implements IValueBinder
             if ($value instanceof DateTimeInterface) {
                 $value = $value->format('Y-m-d H:i:s');
             } elseif (!($value instanceof RichText)) {
+                // Attempt to cast any unexpected objects to string
                 $value = (string) $value;
             }
         }

tests/PhpSpreadsheetTests/Cell/AdvancedValueBinderTest.php

@@ -9,6 +9,7 @@ use PhpOffice\PhpSpreadsheet\Collection\Cells;
 use PhpOffice\PhpSpreadsheet\Shared\StringHelper;
 use PhpOffice\PhpSpreadsheet\Style\NumberFormat;
 use PhpOffice\PhpSpreadsheet\Worksheet\Worksheet;
+use PHPUnit\Framework\MockObject\MockObject;
 use PHPUnit\Framework\TestCase;
 
 class AdvancedValueBinderTest extends TestCase
@@ -42,6 +43,23 @@ class AdvancedValueBinderTest extends TestCase
         StringHelper::setThousandsSeparator($this->thousandsSeparator);
     }
 
+    public function testNullValue()
+    {
+        /** @var Cell&MockObject $cellStub */
+        $cellStub = $this->getMockBuilder(Cell::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        // Configure the stub.
+        $cellStub->expects(self::once())
+            ->method('setValueExplicit')
+            ->with(null, DataType::TYPE_NULL)
+            ->willReturn(true);
+
+        $binder = new AdvancedValueBinder();
+        $binder->bindValue($cellStub, null);
+    }
+
     /**
      * @dataProvider currencyProvider
      *
@@ -105,6 +123,7 @@ class AdvancedValueBinderTest extends TestCase
             ['€2.020,20', 2020.2, $currencyEURO, '.', ',', '€'],
             ['€ 2.020,20', 2020.2, $currencyEURO, '.', ',', '€'],
             ['€2,020.22', 2020.22, $currencyEURO, ',', '.', '€'],
+            ['$10.11', 10.11, $currencyUSD, ',', '.', '€'],
         ];
     }
 

tests/data/Cell/DefaultValueBinder.php

@@ -77,4 +77,8 @@ return [
         's',
         '123456\n',
     ],
+    'Numeric that exceeds PHP MAX_INT Size' => [
+        's',
+        '1234567890123459012345689012345690',
+    ]
 ];