diff --git a/library/Vendors/ChartDirector/phpchartdir.php b/library/Vendors/ChartDirector/phpchartdir.php
index 3702790a8..ad12ef7ca 100644
--- a/library/Vendors/ChartDirector/phpchartdir.php
+++ b/library/Vendors/ChartDirector/phpchartdir.php
@@ -2529,7 +2529,7 @@ class XYChart extends BaseChart {
 	}
 
 	function addBarLayer($data = Null, $color = -1, $name = "", $depth = 0) {
-		if ($data != Null)
+		if (!is_null($data))
 			return new BarLayer(callmethod("XYChart.addBarLayer", $this->ptr, $data, $color, $name, $depth));
 		else
 			return $this->addBarLayer2();
@@ -2541,7 +2541,7 @@ class XYChart extends BaseChart {
 		return new BarLayer(callmethod("XYChart.addBarLayer3", $this->ptr, $data, $colors, $names, $depth));
 	}
 	function addLineLayer($data = Null, $color = -1, $name = "", $depth = 0) {
-		if ($data != Null)
+		if (!is_null($data))
 			return new LineLayer(callmethod("XYChart.addLineLayer", $this->ptr, $data, $color, $name, $depth));
 		else
 			return $this->addLineLayer2();
@@ -2550,7 +2550,7 @@ class XYChart extends BaseChart {
 		return new LineLayer(callmethod("XYChart.addLineLayer2", $this->ptr, $dataCombineMethod, $depth));
 	}
 	function addAreaLayer($data = Null, $color = -1, $name = "", $depth = 0) {
-		if ($data != Null)
+		if (!is_null($data))
 			return new AreaLayer(callmethod("XYChart.addAreaLayer", $this->ptr, $data, $color, $name, $depth));
 		else
 			return $this->addAreaLayer2();
@@ -2559,7 +2559,7 @@ class XYChart extends BaseChart {
 		return new AreaLayer(callmethod("XYChart.addAreaLayer2", $this->ptr, $dataCombineMethod, $depth));
 	}
 	function addHLOCLayer($highData = Null, $lowData = Null, $openData = Null, $closeData = Null, $color = -1) {
-		if ($highData != Null)
+		if (!is_null($highData))
 			return $this->addHLOCLayer3($highData, $lowData, $openData, $closeData, $color, $color);
 		else
 			return $this->addHLOCLayer2();