Review

The method PdfLayer.getAsString() is invoked and the result is immediately converted toUnicodeString(), without checking whether it is null. From the documentation og getAsString() we take that this is unsafe:
"Returns a PdfObject as a PdfString, resolving indirect references. The object associated with the PdfName given is retrieved and resolved to a direct object. If it is a PdfString, it is cast down and returned as such. Otherwise null is returned."

• missing/condition/value_or_state

com/itextpdf/text/pdf/PdfLayer.java

addChild(PdfLayer)

class PdfLayer {
    /**
     * Adds a child layer. Nested layers can only have one parent.
     * @param child the child layer
     */
    public void addChild(PdfLayer child) {
        if (child.parent != null)
            throw new IllegalArgumentException(MessageLocalization.getComposedMessage("the.layer.1.already.has.a.parent", child.getAsString(PdfName.NAME).toUnicodeString()));
        child.parent = this;
        if (children == null)
            children = new ArrayList<PdfLayer>();
        children.add(child);
    }

}