Fix NPE in case keep together is set as default property

DEVSIX-1245

Author: IdamkinI

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

@@ -183,8 +183,13 @@ public void addChild(IRenderer renderer) {
                             } else if (null != result.getCauseOfNothing() && Boolean.TRUE.equals(result.getCauseOfNothing().<Boolean>getProperty(Property.KEEP_TOGETHER))) {
                                 // set KEEP_TOGETHER false on the deepest parent (maybe the element itself) to have KEEP_TOGETHER == true
                                 IRenderer theDeepestKeptTogether = result.getCauseOfNothing();
+                                IRenderer parent;
                                 while (null == theDeepestKeptTogether.getModelElement() || null == theDeepestKeptTogether.getModelElement().<Boolean>getOwnProperty(Property.KEEP_TOGETHER)) {
-                                    theDeepestKeptTogether = ((AbstractRenderer) theDeepestKeptTogether).parent;
+                                    parent = ((AbstractRenderer) theDeepestKeptTogether).parent;
+                                    if (parent == null) {
+                                        break;
+                                    }
+                                    theDeepestKeptTogether = parent;
                                 }
                                 theDeepestKeptTogether.getModelElement().setProperty(Property.KEEP_TOGETHER, false);
                                 Logger logger = LoggerFactory.getLogger(RootRenderer.class);

layout/src/test/java/com/itextpdf/layout/KeepTogetherTest.java

@@ -54,12 +54,14 @@ This file is part of the iText (R) project.
 import com.itextpdf.layout.element.List;
 import com.itextpdf.layout.element.Paragraph;
 import com.itextpdf.layout.property.ListNumberingType;
+import com.itextpdf.layout.property.Property;
 import com.itextpdf.test.ExtendedITextTest;
 import com.itextpdf.test.annotations.LogMessage;
 import com.itextpdf.test.annotations.LogMessages;
 import com.itextpdf.test.annotations.type.IntegrationTest;
 import org.junit.Assert;
 import org.junit.BeforeClass;
+import org.junit.Ignore;
 import org.junit.Test;
 import org.junit.experimental.categories.Category;
 
@@ -229,5 +231,37 @@ public void keepTogetherDivTest02() throws IOException, InterruptedException {
         Assert.assertNull(new CompareTool().compareByContent(outFile, cmpFileName, destinationFolder, "diff"));
     }
 
+    @Test
+    @LogMessages(messages = {
+            @LogMessage(messageTemplate = LogMessageConstant.ELEMENT_DOES_NOT_FIT_AREA)
+    })
+    public void keepTogetherDefaultTest01() throws IOException, InterruptedException {
+        String cmpFileName = sourceFolder + "cmp_keepTogetherDefaultTest01.pdf";
+        String outFile = destinationFolder + "keepTogetherDefaultTest01.pdf";
+
+        PdfDocument pdfDoc = new PdfDocument(new PdfWriter(outFile));
+        Document doc = new Document(pdfDoc);
+
+        Div div = new KeepTogetherDiv();
+        doc.add(new Paragraph("first string"));
+        for (int i = 0; i < 130; i++) {
+            div.add(new Paragraph("String number " + i));
+        }
+
+        doc.add(div);
+        doc.close();
+        Assert.assertNull(new CompareTool().compareByContent(outFile, cmpFileName, destinationFolder, "diff"));
+    }
+
+    private static class KeepTogetherDiv extends Div {
+        @Override
+        public <T1> T1 getDefaultProperty(int property) {
+            if (property == Property.KEEP_TOGETHER) {
+                return (T1) (Object) true;
+            }
+            return super.<T1>getDefaultProperty(property);
+        }
+    }
+
 
 }