apache/druid · error · IllegalArgumentException

parameter cannot be a blank string

Error message

%s parameter cannot be a blank string

What it means

CatalogUtils.getNonBlankString reads a string-valued parameter from a catalog/model argument map and rejects it when the value, after trimming, is empty. The catalog model layer requires meaningful non-blank values for such parameters (e.g. table or column properties), so whitespace-only strings are treated as invalid even though they are not null.

Solutions

1. Set the named parameter to a non-blank string value in the catalog spec or argument map.
2. If the parameter is optional, remove the key entirely instead of supplying an empty string (getNonBlankString returns null for absent keys).
3. Trim-check user input before submitting the catalog definition: if (s == null || s.trim().isEmpty()) fail fast with a clearer message.

Example fix

// before
{"properties": {"name": "   "}}
// after
{"properties": {"name": "my_table"}}

Object v = args.get("param");
if (v instanceof String && ((String) v).trim().isEmpty()) {
  throw new IllegalArgumentException("param must be a non-blank string or omitted");
}

boolean isPresentNonBlank(Object v) { return v instanceof String && !((String) v).trim().isEmpty(); }

try { String s = CatalogUtils.getNonBlankString(args, "param"); ... } catch (IllegalArgumentException e) { log.error("Invalid catalog parameter: %s", e.getMessage()); }

When it happens

Trigger: Calling getNonBlankString(args, "x") where args.get("x") is "", " ", or any whitespace-only string. Also occurs via CatalogUtils validation paths that call getNonBlankString on user-supplied catalog spec properties.

Common situations: A user defines a catalog table or column spec in JSON/YAML and leaves a required property set to an empty string (e.g. "description": "" or "name": ""); copy-paste of config that wiped a value; templating that substituted an empty variable.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

• A table definition must include a table spec.
• An external HTTP table with a URI must also provide the…
• An external HTTP table with a URI must also provide the…
• An external S3 table with a format must also provide the…
• At least one of baseDir or files should be specified

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/d293d1e1cfc691d3. Report an issue: GitHub.

Appendix: source

Thrown at server/src/main/java/org/apache/druid/catalog/model/CatalogUtils.java:210

  )
  {
    return Stream
        .of(base, additions)
        .filter(Objects::nonNull)
        .flatMap(Collection::stream)
        .collect(Collectors.toList());
  }

  /**
   * Get a string parameter that can either be null or non-blank.
   */
  public static String getNonBlankString(Map<String, Object> args, String parameter)
  {
    String value = CatalogUtils.getString(args, parameter);
    if (value != null) {
      value = value.trim();
      if (value.isEmpty()) {
        throw new IAE("%s parameter cannot be a blank string", parameter);
      }
    }
    return value;
  }

  public static List<String> getUriListArg(Map<String, Object> args, String parameter)
  {
    String urisString = CatalogUtils.getString(args, parameter);
    if (Strings.isNullOrEmpty(urisString)) {
      throw new IAE("One or more values are required for parameter %s", parameter);
    }
    return stringToList(urisString);
  }

  public static List<URI> stringToUriList(String uris)
  {
    return stringListToUriList(stringToList(uris));
  }

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