In the method AbstractSplitDockingGrid.addPlaceholders method, there is a bug causing null values to be introduced if oldPlaceholders.length > placeholders.length. I’m using version 1.1.2p20a.
On line 278:
System.arraycopy( oldPlaceholders, 0, node.placeholders, 0, placeholders.length );
Should be:
System.arraycopy( oldPlaceholders, 0, node.placeholders, 0, oldPlaceholders.length );