Fix NullPointerException in AbstractRenderer class and update createXObject method

DEVSIX-4138

Author: introfog

layout/src/main/java/com/itextpdf/layout/renderer/AbstractRenderer.java

@@ -49,7 +49,6 @@ This file is part of the iText (R) project.
 import com.itextpdf.kernel.PdfException;
 import com.itextpdf.kernel.colors.Color;
 import com.itextpdf.kernel.colors.gradients.AbstractLinearGradientBuilder;
-import com.itextpdf.kernel.colors.gradients.StrategyBasedLinearGradientBuilder;
 import com.itextpdf.kernel.font.PdfFont;
 import com.itextpdf.kernel.geom.AffineTransform;
 import com.itextpdf.kernel.geom.Point;
@@ -538,7 +537,8 @@ public void drawBackground(DrawContext drawContext) {
                     //  for gradient uses width and height = 1. For all othe cases the logic left as it was.
                     Rectangle imageRectangle;
                     if (backgroundXObject == null) {
-                        backgroundXObject = createXObject(backgroundImage.getLinearGradientBuilder(), backgroundArea, drawContext.getDocument());
+                        backgroundXObject = AbstractRenderer.createXObject(backgroundImage.getLinearGradientBuilder(),
+                                backgroundArea, drawContext.getDocument());
                         imageRectangle = new Rectangle(backgroundArea.getX(), backgroundArea.getTop() - backgroundXObject.getHeight(),1, 1);
                     } else {
                          imageRectangle = new Rectangle(backgroundArea.getX(), backgroundArea.getTop() - backgroundXObject.getHeight(),
@@ -575,20 +575,26 @@ public void drawBackground(DrawContext drawContext) {
         }
     }
 
-    public PdfFormXObject createXObject(AbstractLinearGradientBuilder linearGradientBuilder,
+    /**
+     * Create a {@link PdfFormXObject} with the given area and containing a linear gradient inside.
+     *
+     * @param linearGradientBuilder the linear gradient builder
+     * @param xObjectArea the result object area
+     * @param document the pdf document
+     * @return the xObject with a specified area and a linear gradient
+     */
+    public static PdfFormXObject createXObject(AbstractLinearGradientBuilder linearGradientBuilder,
             Rectangle xObjectArea, PdfDocument document) {
-        if (linearGradientBuilder == null) {
-            return null;
-        }
         Rectangle formBBox = new Rectangle(0, 0, xObjectArea.getWidth(), xObjectArea.getHeight());
-        PdfFormXObject xObject = null;
-        Color gradientColor = linearGradientBuilder.buildColor(formBBox, null);
-        if (gradientColor != null) {
-            xObject = new PdfFormXObject(formBBox);
-            new PdfCanvas(xObject, document)
-                    .setColor(gradientColor, true)
-                    .rectangle(formBBox)
-                    .fill();
+        PdfFormXObject xObject = new PdfFormXObject(formBBox);
+        if (linearGradientBuilder != null) {
+            Color gradientColor = linearGradientBuilder.buildColor(formBBox, null);
+            if (gradientColor != null) {
+                new PdfCanvas(xObject, document)
+                        .setColor(gradientColor, true)
+                        .rectangle(formBBox)
+                        .fill();
+            }
         }
         return xObject;
     }

layout/src/test/java/com/itextpdf/layout/renderer/AbstractRendererTest.java

@@ -0,0 +1,50 @@
+package com.itextpdf.layout.renderer;
+
+import com.itextpdf.io.source.ByteArrayOutputStream;
+import com.itextpdf.kernel.colors.ColorConstants;
+import com.itextpdf.kernel.colors.gradients.AbstractLinearGradientBuilder;
+import com.itextpdf.kernel.colors.gradients.GradientColorStop;
+import com.itextpdf.kernel.colors.gradients.GradientColorStop.OffsetType;
+import com.itextpdf.kernel.colors.gradients.StrategyBasedLinearGradientBuilder;
+import com.itextpdf.kernel.geom.Rectangle;
+import com.itextpdf.kernel.pdf.PdfDocument;
+import com.itextpdf.kernel.pdf.PdfName;
+import com.itextpdf.kernel.pdf.PdfWriter;
+import com.itextpdf.kernel.pdf.xobject.PdfXObject;
+import com.itextpdf.test.ExtendedITextTest;
+import com.itextpdf.test.annotations.type.UnitTest;
+
+import org.junit.Assert;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+
+@Category(UnitTest.class)
+public class AbstractRendererTest extends ExtendedITextTest {
+    @Test
+    public void createXObjectTest() {
+        AbstractLinearGradientBuilder gradientBuilder = new StrategyBasedLinearGradientBuilder()
+                .setGradientDirectionAsStrategy(StrategyBasedLinearGradientBuilder.GradientStrategy.TO_BOTTOM_LEFT)
+                .addColorStop(new GradientColorStop(ColorConstants.RED.getColorValue(), 0d, OffsetType.RELATIVE))
+                .addColorStop(new GradientColorStop(ColorConstants.GREEN.getColorValue(), 0.5, OffsetType.RELATIVE));
+
+        PdfDocument pdfDocument = new PdfDocument(new PdfWriter(new ByteArrayOutputStream()));
+        PdfXObject pdfXObject = AbstractRenderer.createXObject(gradientBuilder, new Rectangle(0, 0, 20, 20), pdfDocument);
+        Assert.assertNotNull(pdfXObject.getPdfObject().get(PdfName.Resources));
+    }
+
+    @Test
+    public void createXObjectWithNullLinearGradientTest() {
+        PdfDocument pdfDocument = new PdfDocument(new PdfWriter(new ByteArrayOutputStream()));
+        PdfXObject pdfXObject = AbstractRenderer.createXObject(null, new Rectangle(0, 0, 20, 20), pdfDocument);
+        Assert.assertNull(pdfXObject.getPdfObject().get(PdfName.Resources));
+    }
+
+    @Test
+    public void createXObjectWithInvalidColorTest() {
+        AbstractLinearGradientBuilder gradientBuilder = new StrategyBasedLinearGradientBuilder();
+
+        PdfDocument pdfDocument = new PdfDocument(new PdfWriter(new ByteArrayOutputStream()));
+        PdfXObject pdfXObject = AbstractRenderer.createXObject(gradientBuilder, new Rectangle(0, 0, 20, 20), pdfDocument);
+        Assert.assertNull(pdfXObject.getPdfObject().get(PdfName.Resources));
+    }
+}