private void insertDocumentIfNotExists(String fileURI) {
        if (documentDiagnostics.containsKey(fileURI)) return;
        documentDiagnostics.put(fileURI, new ArrayList<>());
    }
SchemaDiagnosticHandler is a wrapper for publishing diagnostics to the client
integration/schema-language-server/language-server/src/main/java/ai/vespa/schemals/SchemaDiagnosticsHandler.java