diff --git a/CHANGELOG.md b/CHANGELOG.md
index 290474a1..a7082cf9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -21,6 +21,8 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 
 ### Changed
 
+- Better enforcement of value modification to match specified datatype when using setValueExplicit() 
+- Relax validation of merge cells to allow merge for a single cell reference [Issue #2776](https://github.com/PHPOffice/PhpSpreadsheet/issues/2776)
 - Memory and speed improvements, particularly for the Cell Collection, and the Writers.
 
   See [the Discussion section on github](https://github.com/PHPOffice/PhpSpreadsheet/discussions/2821) for details of performance across versions
diff --git a/src/PhpSpreadsheet/Cell/Cell.php b/src/PhpSpreadsheet/Cell/Cell.php
index 76d5e86d..2005694d 100644
--- a/src/PhpSpreadsheet/Cell/Cell.php
+++ b/src/PhpSpreadsheet/Cell/Cell.php
@@ -202,6 +202,11 @@ class Cell
      *
      * @param mixed $value Value
      * @param string $dataType Explicit data type, see DataType::TYPE_*
+     *        Note that PhpSpreadsheet does not validate that the value and datatype are consistent, in using this
+     *             method, then it is your responsibility as an end-user developer to validate that the value and
+     *             the datatype match.
+     *       If you do mismatch value and datatpe, then the value you enter may be changed to match the datatype
+     *          that you specify.
      *
      * @return Cell
      */
@@ -210,7 +215,7 @@ class Cell
         // set the value according to data type
         switch ($dataType) {
             case DataType::TYPE_NULL:
-                $this->value = $value;
+                $this->value = null;
 
                 break;
             case DataType::TYPE_STRING2:
diff --git a/src/PhpSpreadsheet/Cell/DataType.php b/src/PhpSpreadsheet/Cell/DataType.php
index 0f7efe2a..390dcde5 100644
--- a/src/PhpSpreadsheet/Cell/DataType.php
+++ b/src/PhpSpreadsheet/Cell/DataType.php
@@ -48,7 +48,7 @@ class DataType
      *
      * @param null|RichText|string $textValue Value to sanitize to an Excel string
      *
-     * @return null|RichText|string Sanitized value
+     * @return RichText|string Sanitized value
      */
     public static function checkString($textValue)
     {
@@ -58,7 +58,7 @@ class DataType
         }
 
         // string must never be longer than 32,767 characters, truncate if necessary
-        $textValue = StringHelper::substring($textValue, 0, 32767);
+        $textValue = StringHelper::substring((string) $textValue, 0, 32767);
 
         // we require that newline is represented as "\n" in core, not as "\r\n" or "\r"
         $textValue = str_replace(["\r\n", "\r"], "\n", $textValue);
diff --git a/src/PhpSpreadsheet/Worksheet/Worksheet.php b/src/PhpSpreadsheet/Worksheet/Worksheet.php
index f08ddf0c..d047380a 100644
--- a/src/PhpSpreadsheet/Worksheet/Worksheet.php
+++ b/src/PhpSpreadsheet/Worksheet/Worksheet.php
@@ -1177,6 +1177,11 @@ class Worksheet implements IComparable
      *               or as an array of [$columnIndex, $row] (e.g. [3, 5]), or a CellAddress object.
      * @param mixed $value Value of the cell
      * @param string $dataType Explicit data type, see DataType::TYPE_*
+     *        Note that PhpSpreadsheet does not validate that the value and datatype are consistent, in using this
+     *             method, then it is your responsibility as an end-user developer to validate that the value and
+     *             the datatype match.
+     *       If you do mismatch value and datatpe, then the value you enter may be changed to match the datatype
+     *          that you specify.
      *
      * @return $this
      */
@@ -1199,6 +1204,11 @@ class Worksheet implements IComparable
      * @param int $row Numeric row coordinate of the cell
      * @param mixed $value Value of the cell
      * @param string $dataType Explicit data type, see DataType::TYPE_*
+     *        Note that PhpSpreadsheet does not validate that the value and datatype are consistent, in using this
+     *             method, then it is your responsibility as an end-user developer to validate that the value and
+     *             the datatype match.
+     *       If you do mismatch value and datatpe, then the value you enter may be changed to match the datatype
+     *          that you specify.
      *
      * @return $this
      */
@@ -1770,6 +1780,10 @@ class Worksheet implements IComparable
         $numberRows = $lastRow - $firstRow;
         $numberColumns = $lastColumnIndex - $firstColumnIndex;
 
+        if ($numberRows === 1 && $numberColumns === 1) {
+            return $this;
+        }
+
         // create upper left cell if it does not already exist
         $upperLeft = "{$firstColumn}{$firstRow}";
         if (!$this->cellExists($upperLeft)) {