Prevent null from being passed as occupied area in case of FULL

In case result is updated to be FULL, result's occupied area could be null:
one should check the splitRenderer's occupied area instead.

DEVSIX-5237

Author: ars18wrw

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

@@ -46,6 +46,7 @@ This file is part of the iText (R) project.
 import com.itextpdf.kernel.geom.Rectangle;
 import com.itextpdf.layout.borders.Border;
 import com.itextpdf.layout.element.Div;
+import com.itextpdf.layout.layout.LayoutArea;
 import com.itextpdf.layout.layout.LayoutContext;
 import com.itextpdf.layout.layout.LayoutResult;
 import com.itextpdf.layout.margincollapse.MarginsCollapseHandler;
@@ -235,7 +236,8 @@ LayoutResult processNotFullChildResult(LayoutContext layoutContext,
             if (splitRenderer != null) {
                 splitRenderer.setChildRenderers(getChildRenderers());
             }
-            return new LayoutResult(LayoutResult.FULL, result.getOccupiedArea(), splitRenderer, null, null);
+            return new LayoutResult(LayoutResult.FULL,
+                    getOccupiedAreaInCaseNothingWasWrappedWithFull(result, splitRenderer), splitRenderer, null, null);
         } else {
             applyPaddings(occupiedArea.getBBox(), paddings, true);
             applyBorderBox(occupiedArea.getBBox(), borders, true);
@@ -250,6 +252,11 @@ LayoutResult processNotFullChildResult(LayoutContext layoutContext,
         }
     }
 
+    // TODO DEVSIX-5238 Consider this fix (perhaps it should be improved or unified) while working on the ticket
+    LayoutArea getOccupiedAreaInCaseNothingWasWrappedWithFull(LayoutResult result, IRenderer splitRenderer) {
+        return null != result.getOccupiedArea() ? result.getOccupiedArea() : splitRenderer.getOccupiedArea();
+    }
+
     @Override
     boolean stopLayoutingChildrenIfChildResultNotFull(LayoutResult returnResult) {
         return returnResult.getStatus() != LayoutResult.FULL;

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

@@ -22,12 +22,17 @@ This file is part of the iText (R) project.
  */
 package com.itextpdf.layout.renderer;
 
+import com.itextpdf.kernel.geom.Rectangle;
 import com.itextpdf.layout.borders.SolidBorder;
 import com.itextpdf.layout.element.Div;
+import com.itextpdf.layout.layout.LayoutArea;
+import com.itextpdf.layout.layout.LayoutContext;
+import com.itextpdf.layout.layout.LayoutResult;
 import com.itextpdf.layout.property.Property;
 import com.itextpdf.layout.property.UnitValue;
 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;
@@ -176,6 +181,17 @@ public void widthSetToChildManyChildrenFlexRendererWithMinWidthTest() {
         Assert.assertEquals(125F, flexRenderer.getMinMaxWidth().getMaxWidth(), EPS);
     }
 
+
+    @Test
+    public void decreaseLayoutBoxAfterChildPlacementResultsOccupiedAreaNull() {
+        FlexContainerRenderer splitRenderer = new FlexContainerRenderer(new Div());
+        splitRenderer.occupiedArea = new LayoutArea(0, new Rectangle(0, 0));
+
+        LayoutResult nothing = new LayoutResult(LayoutResult.NOTHING, null, splitRenderer, null);
+        Assert.assertNotNull(new FlexContainerRenderer(new Div())
+                .getOccupiedAreaInCaseNothingWasWrappedWithFull(nothing, splitRenderer));
+    }
+
     @Test
     public void widthSetToChildManyChildrenFlexRendererWithMinWidthBiggerThanMaxWidthTest() {
         FlexContainerRenderer flexRenderer = new FlexContainerRenderer(new Div());