apache/cassandra · error · InvalidRequestException

Cannot set to empty string

Error message

Cannot set %s to empty string

What it means

Schema description comments (e.g. WITH comment = ... on keyspaces/tables) may not be the empty string; an empty description is treated as invalid rather than as 'remove the comment'. SchemaDescriptionStatement.validate() throws InvalidRequestException with the description type name (e.g. 'Comment').

Solutions

1. Omit the comment option in ALTER to remove it (the statement path that ignores removal)
2. Set a non-empty comment string

Example fix

// before
ALTER TABLE t WITH comment = '';
// after
ALTER TABLE t;  -- or WITH comment = 'user table metadata'

if (typeof comment === 'string' && comment.length === 0) {
  delete ddl.comment; // treat empty as 'no comment'
}

When it happens

Trigger: ALTER KEYSPACE/ALTER TABLE ... WITH comment = '' ; or CREATE ... WITH comment = ''.

Common situations: Trying to clear a comment by setting it to empty string (correct way: omit the comment option entirely or set it to null/absent so the statement removes it); automated schema generation producing ''.

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

• Cannot add new field
• Configuration for at least one datacenter must be present
• ACCESS TO DATACENTERS operations not supported by…
• Accord transactions are disabled on table (table is being…
• Aggregate name ' ' is invalid

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/1e42b3650e5dbb88. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/cql3/statements/schema/SchemaDescriptionStatement.java:59

    {
        super(keyspaceName);
        this.description = comment;
        this.descriptionType = descriptionType;
    }

    @Override
    public void validate(ClientState state)
    {
        super.validate(state);
        if(description == null)
        {
            // Statement is removing comment on schema elements, ignore
            return;
        }

        if(description.isEmpty())
        {
            throw new InvalidRequestException(String.format("Cannot set %s to empty string", descriptionType.value));
        }

        if (description.length() > descriptionType.maxLength)
        {
            String msg = String.format("%s length (%d) exceeds maximum allowed length (%d)",
                                       descriptionType.value,
                                       description.length(),
                                       descriptionType.maxLength);
            throw new InvalidRequestException(msg);
        }
    }

    protected KeyspaceMetadata validateAndGetKeyspace(Keyspaces schema)
    {
        KeyspaceMetadata keyspace = schema.getNullable(keyspaceName);

        if (null == keyspace)
            throw ire("Keyspace '%s' doesn't exist", keyspaceName);

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