diff --git a/bundles/plugins/org.bonitasoft.studio.expression.editor/src/org/bonitasoft/studio/expression/editor/viewer/ExpressionCollectionViewer.java b/bundles/plugins/org.bonitasoft.studio.expression.editor/src/org/bonitasoft/studio/expression/editor/viewer/ExpressionCollectionViewer.java
index fccc4003180ab4fbce67cb6ffc2ef7df17d4d700..f2b39f1204b5c44c27ab8f364fe0c6351e87ba16 100644
--- a/bundles/plugins/org.bonitasoft.studio.expression.editor/src/org/bonitasoft/studio/expression/editor/viewer/ExpressionCollectionViewer.java
+++ b/bundles/plugins/org.bonitasoft.studio.expression.editor/src/org/bonitasoft/studio/expression/editor/viewer/ExpressionCollectionViewer.java
@@ -299,7 +299,7 @@ public class ExpressionCollectionViewer implements IBonitaVariableContext {
         } else {
             buttonComposite = new Composite(parent, SWT.NONE);
         }
-        final int topIndent = captions.isEmpty() ? 0 : 15;
+        final int topIndent = captions == null || captions.isEmpty() ? 0 : 15;
         buttonComposite.setLayoutData(GridDataFactory.fillDefaults().grab(false, false).align(SWT.FILL, SWT.TOP).indent(0, topIndent).create());
 
         final RowLayout rl = new RowLayout(SWT.VERTICAL);