The following exception can occur in the GraphBuilder when ZNAP is selected as target format
java.lang.NullPointerException
        at org.esa.snap.dataio.znap.ZnapProductWriter.close(ZnapProductWriter.java:229)
        at org.esa.snap.core.datamodel.Product.closeProductWriter(Product.java:666)
        at org.esa.snap.core.datamodel.Product.closeIO(Product.java:690)
        at org.esa.snap.core.datamodel.Product.dispose(Product.java:716)
        at org.esa.snap.core.gpf.graph.NodeContext.dispose(NodeContext.java:173)
        at org.esa.snap.core.gpf.graph.GraphContext.dispose(GraphContext.java:210)
        at org.esa.snap.graphbuilder.rcp.dialogs.support.GraphExecuter.recreateGraphContext(GraphExecuter.java:275)

In the close method of the ZnapProductWriter class the zarrStore is null.
This happens only if the product wasn’t written because the store is only created when needed.

A simple null check should fix this.

As a workaround for users:
First set up the graph and when done select ZNAP as target format. Then the execution should work.