private void setupDocumentProcessing(ContentCluster c, ModelElement e) {
            String docprocCluster = e.stringAttribute("cluster");
            if (docprocCluster != null) {
                docprocCluster = docprocCluster.trim();
            }
            String docprocChain = e.stringAttribute("chain");
            if (docprocChain != null) {
                docprocChain = docprocChain.trim();
            }
            if (docprocCluster != null && !docprocCluster.isEmpty()) {
                c.getSearch().getIndexingDocproc().setClusterName(docprocCluster);
            }
            if (docprocChain != null && !docprocChain.isEmpty()) {
                c.getSearch().getIndexingDocproc().setChainName(docprocChain);
            }
        }
The admin model of this system or null if none (which only happens in tests)
config-model/src/main/java/com/yahoo/vespa/model/content/cluster/ContentCluster.java