apache/shardingsphere · error · MCPInvalidRequestException

object_types cannot contain blank values.

Error message

object_types cannot contain blank values.

What it means

Thrown by MCPToolArguments.resolveObjectType as MCPInvalidRequestException when an object_types array entry trims to an empty string. Blank entries (empty strings or whitespace-only) are rejected explicitly so a silently ignored filter value cannot cause an unexpected metadata scope.

Source

Thrown at mcp/core/src/main/java/org/apache/shardingsphere/mcp/core/tool/request/MCPToolArguments.java:72

        }
        if (!(rawValue instanceof Collection)) {
            throw new MCPInvalidRequestException("object_types must be an array.");
        }
        Collection<?> objectTypes = (Collection<?>) rawValue;
        if (objectTypes.isEmpty()) {
            return Collections.emptySet();
        }
        Set<SupportedMCPMetadataObjectType> result = new LinkedHashSet<>(objectTypes.size(), 1F);
        for (Object each : objectTypes) {
            result.add(resolveObjectType(each, supportedObjectTypes));
        }
        return result;
    }
    
    private SupportedMCPMetadataObjectType resolveObjectType(final Object objectType, final Set<SupportedMCPMetadataObjectType> supportedObjectTypes) {
        String actualValue = Objects.toString(objectType, "").trim();
        if (actualValue.isEmpty()) {
            throw new MCPInvalidRequestException("object_types cannot contain blank values.");
        }
        try {
            SupportedMCPMetadataObjectType result = SupportedMCPMetadataObjectType.valueOf(actualValue.toUpperCase(Locale.ENGLISH));
            if (supportedObjectTypes.contains(result)) {
                return result;
            }
        } catch (final IllegalArgumentException ignored) {
        }
        throw new MCPInvalidMetadataObjectTypesException(actualValue, createAllowedObjectTypes(supportedObjectTypes));
    }
    
    private List<String> createAllowedObjectTypes(final Set<SupportedMCPMetadataObjectType> supportedObjectTypes) {
        return supportedObjectTypes.stream().map(each -> each.name().toLowerCase(Locale.ENGLISH)).toList();
    }
    
    /**
     * Get string argument.
     *

View on GitHub (pinned to e952770a21)

Solutions

1. Filter out null/blank entries before sending: array.filter(s => s && s.trim())
2. Fix the source of the empty entries (trailing commas, unfilled form fields)
3. If no filtering is desired, omit object_types entirely — absence returns the empty/full default per the tool contract

Example fix

// before
args.object_types = "table,".split(",")  // ["table", ""]

// after
args.object_types = "table,".split(",").filter(s => s.trim());  // ["table"]

List<String> cleaned = raw.stream().filter(Objects::nonNull).map(String::trim).filter(s -> !s.isEmpty()).distinct().toList();
if (cleaned.size() != raw.size()) arguments.put("object_types", cleaned);

try {
    listMetadata(arguments);
} catch (MCPInvalidRequestException e) {
    if (e.getMessage().contains("blank values")) listMetadata(Map.of("object_types", stripBlanks((List<?>) arguments.get("object_types"))));
}

When it happens

Trigger: Objects.toString(objectType, "").trim().isEmpty() for any array element — e.g. {"object_types": ["table", ""]}, [" "], or a null element inside the array.

Common situations: Client-side array building that leaves trailing empty entries (split of a trailing comma: "table,".split(",")); form inputs submitted with an empty selection; agent-generated lists containing nulls.

Related errors

• object_types must be an array.
• Unsupported object_types value `%s`.
• Statement is not a transaction command.
• %s must be an integer between %d and %d.
• Metadata introspection SQL should use MCP metadata resources

AI-assisted analysis of apache/shardingsphere@e952770a21 (2026-08-14). Data as JSON: /api/errors/b10cbec73ad67407. Report an issue: GitHub.