Fix NPE in collapse margin logic.

DEVSIX-1195

Autoported commit.
Original commit hash: [6050baf43]

Author: pavel-alay

itext/itext.layout/itext/layout/margincollapse/MarginsCollapseHandler.cs

@@ -225,7 +225,9 @@ public virtual void EndMarginsCollapse(Rectangle layoutBox) {
             else {
                 ownCollapseAfter = new MarginsCollapse();
             }
-            ownCollapseAfter.JoinMargin(GetModelBottomMargin(renderer));
+            if (ownCollapseAfter != null) {
+                ownCollapseAfter.JoinMargin(GetModelBottomMargin(renderer));
+            }
             collapseInfo.SetOwnCollapseAfter(ownCollapseAfter);
             if (collapseInfo.IsSelfCollapsing()) {
                 if (prevChildMarginInfo != null) {
@@ -268,7 +270,8 @@ public virtual void EndMarginsCollapse(Rectangle layoutBox) {
         }
 
         private void UpdateCollapseBeforeIfPrevKidIsFirstAndSelfCollapsed(MarginsCollapse collapseAfter) {
-            if (prevChildMarginInfo.IsSelfCollapsing() && prevChildMarginInfo.IsIgnoreOwnMarginTop()) {
+            if (prevChildMarginInfo.IsSelfCollapsing() && prevChildMarginInfo.IsIgnoreOwnMarginTop() && collapseAfter 
+                != null) {
                 // prevChildMarginInfo.isIgnoreOwnMarginTop() is true only if it's the first kid and is adjoined to parent margin
                 collapseInfo.GetCollapseBefore().JoinMargin(collapseAfter);
             }

port-hash

@@ -1 +1 @@
-da5798b5cf162be5c1dd163f02f530299b6e46e3
+6050baf43726dc4ce3100fd436758dce7eaa63e2