diff --git a/Classes/PHPExcel/Calculation.php b/Classes/PHPExcel/Calculation.php
index f71271ed..5de4bb2b 100644
--- a/Classes/PHPExcel/Calculation.php
+++ b/Classes/PHPExcel/Calculation.php
@@ -3085,7 +3085,12 @@ class PHPExcel_Calculation {
 							}
 							$cellRef = PHPExcel_Cell::stringFromColumnIndex(min($oCol)).min($oRow).':'.PHPExcel_Cell::stringFromColumnIndex(max($oCol)).max($oRow);
 							if ($pCellParent !== NULL) {
-								$cellValue = $this->extractCellRange($cellRef, $pCellParent->getParent()->getSheetByName($sheet1), false);
+								$referencedWorksheet = $pCellParent->getParent()->getSheetByName($sheet1);
+								if ($referencedWorksheet) {
+									$cellValue = $this->extractCellRange($cellRef, $referencedWorksheet, false);
+								} else {
+									return $this->_raiseFormulaError('Unable to access Cell Reference');
+								}
 							} else {
 								return $this->_raiseFormulaError('Unable to access Cell Reference');
 							}
@@ -3205,7 +3210,12 @@ class PHPExcel_Calculation {
 //							echo '$cellRef='.$cellRef.' in worksheet '.$matches[2].'<br />';
 							$this->_writeDebug('Evaluating Cell Range '.$cellRef.' in worksheet '.$matches[2]);
 							if ($pCellParent !== NULL) {
-								$cellValue = $this->extractCellRange($cellRef, $pCellParent->getParent()->getSheetByName($matches[2]), false);
+								$referencedWorksheet = $pCellParent->getParent()->getSheetByName($matches[2]);
+								if ($referencedWorksheet) {
+									$cellValue = $this->extractCellRange($cellRef, $pCellParent->getParent()->getSheetByName($matches[2]), false);
+								} else {
+									return $this->_raiseFormulaError('Unable to access Cell Reference');
+								}
 							} else {
 								return $this->_raiseFormulaError('Unable to access Cell Reference');
 							}
@@ -3238,11 +3248,12 @@ class PHPExcel_Calculation {
 //							echo '$cellRef='.$cellRef.' in worksheet '.$matches[2].'<br />';
 							$this->_writeDebug('Evaluating Cell '.$cellRef.' in worksheet '.$matches[2]);
 							if ($pCellParent !== NULL) {
-								if ($pCellParent->getParent()->getSheetByName($matches[2])->cellExists($cellRef)) {
-									$cellValue = $this->extractCellRange($cellRef, $pCellParent->getParent()->getSheetByName($matches[2]), false);
+								$referencedWorksheet = $pCellParent->getParent()->getSheetByName($matches[2]);
+								if (($referencedWorksheet) && ($referencedWorksheet->cellExists($cellRef))) {
+									$cellValue = $this->extractCellRange($cellRef, $referencedWorksheet, false);
 									$pCell->attach($pCellParent);
 								} else {
-									$cellValue = null;
+									$cellValue = NULL;
 								}
 							} else {
 								return $this->_raiseFormulaError('Unable to access Cell Reference');
@@ -3631,7 +3642,7 @@ class PHPExcel_Calculation {
 			if (!isset($aReferences[1])) {
 				//	Single cell in range
 				list($currentCol,$currentRow) = sscanf($aReferences[0],'%[A-Z]%d');
-				if ($pSheet->cellExists($aReferences[0])) {
+				if ($pSheet && $pSheet->cellExists($aReferences[0])) {
 					$returnValue[$currentRow][$currentCol] = $pSheet->getCell($aReferences[0])->getCalculatedValue($resetLog);
 				} else {
 					$returnValue[$currentRow][$currentCol] = null;
@@ -3642,7 +3653,7 @@ class PHPExcel_Calculation {
 					// Extract range
 					list($currentCol,$currentRow) = sscanf($reference,'%[A-Z]%d');
 
-					if ($pSheet->cellExists($reference)) {
+					if ($pSheet && $pSheet->cellExists($reference)) {
 						$returnValue[$currentRow][$currentCol] = $pSheet->getCell($reference)->getCalculatedValue($resetLog);
 					} else {
 						$returnValue[$currentRow][$currentCol] = null;
diff --git a/Tests/34chartupdate.php b/Tests/34chartupdate.php
index 46c73afc..c6021723 100644
--- a/Tests/34chartupdate.php
+++ b/Tests/34chartupdate.php
@@ -49,7 +49,7 @@ if (!file_exists("33chartcreate-bar.xlsx")) {
 echo date('H:i:s') , " Load from Excel2007 file" , EOL;
 $objReader = PHPExcel_IOFactory::createReader("Excel2007");
 $objReader->setIncludeCharts(TRUE);
-$objPHPExcel = $objReader->load("33chartcreate.xlsx");
+$objPHPExcel = $objReader->load("33chartcreate-bar.xlsx");
 
 
 echo date('H:i:s') , " Update cell data values that are displayed in the chart" , EOL;
diff --git a/changelog.txt b/changelog.txt
index 76adc2a8..fbcecf99 100644
--- a/changelog.txt
+++ b/changelog.txt
@@ -84,6 +84,7 @@ Fixed in develop branch:
 - Feature:  (MBaker)     Excel compatibility option added for writing CSV files
                          While Excel 2010 can read CSV files with a simple UTF-8 BOM, Excel2007 and earlier require UTF-16LE encoded tab-separated files.
                          The new setExcelCompatibility(TRUE) option for the CSV Writer will generate files with this formatting for easy import into Excel2007 and below.
+- Feature:  (MBaker)     Language implementations for Turkish (tr)
 - General:  (alexgann)   Add Currency detection to the Advanced Value Binder
 - General:  (MBaker)     Work item 18404 - setCellValueExplicitByColumnAndRow() do not return PHPExcel_Worksheet
 - General:  (MBaker)     Work item 18324 - Reader factory doesn't read anymore XLTX and XLT files