public Builder requiredPermissions(final Set<DocumentPermission> requiredPermissions) {
            if (requiredPermissions == null) {
                this.requiredPermissions = null;
            } else {
                this.requiredPermissions = new HashSet<>(requiredPermissions);
            }
            return this;
        }
Set the document types of root nodes to include. If null/empty return all root notes.
stroom-core-shared/src/main/java/stroom/explorer/shared/ExplorerTreeFilter.java