airbnb/epoxy · error · EpoxyProcessorException

Attributes cannot be empty

Error message

Attributes cannot be empty

What it means

GeneratedModelInfo.AttributeGroup is an internal processor invariant: every attribute group must contain at least one AttributeInfo. An empty attributes list means the processor assembled a group with no attributes, indicating a bug or malformed model input, so it throws 'Attributes cannot be empty' via buildEpoxyException. Reached from addAttributeGroup while generating model info.

Solutions

1. Check the model class that triggered the failure: ensure at least one attribute is actually declarable/visible to the processor (not all filtered out by annotations or visibility)
2. If you build AttributeGroup in custom code, guard with require(attributes.isNotEmpty()) before constructing
3. Update or bisect the Epoxy processor version — if a valid model triggers this, it is a processor bug worth reporting with a minimal reproducer
4. Clear build caches / run a clean build to rule out stale generated model info

Example fix

// before (custom processor code)
addAttributeGroup(groupName, attributes)
// after
if (attributes.isNotEmpty()) {
    addAttributeGroup(groupName, attributes)
}

// caller-side check before registering a group
require(attributes.isNotEmpty()) { "Attribute group '$groupName' has no attributes" }

When it happens

Trigger: addAttributeGroup is called (directly or via processor model parsing) with an empty List<AttributeInfo>, e.g. when a model class's attributes were all filtered out before grouping but the group was still registered.

Common situations: Custom processor extensions or forks that construct AttributeGroup manually; model classes where attribute collection logic yields nothing (e.g. all attributes excluded) but a group name is still provided; internal Epoxy processor bugs after version upgrades.

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

• Default attribute has no default code
• Nullability has not been set
• Failed to create regex for resource reference…
• Please use value or code explicitly
• You must set an id on a model before adding it. Use the…

AI-assisted analysis of airbnb/epoxy@e45bd3a61f (2026-09-13). Data as JSON: /api/errors/0e1e6e9a96c6a9b5. Report an issue: GitHub.

Appendix: source

Thrown at epoxy-processor/src/main/java/com/airbnb/epoxy/processor/GeneratedModelInfo.kt:261

    }

    fun attributeGroup(attribute: AttributeInfo): AttributeGroup? {
        return attributeToGroup[attribute]
    }

    class AttributeGroup internal constructor(
        groupName: String?,
        attributes: List<AttributeInfo>,
        defaultAttribute: AttributeInfo?
    ) {
        val name: String?
        val attributes: List<AttributeInfo>
        val isRequired: Boolean
        val defaultAttribute: AttributeInfo?

        init {
            if (attributes.isEmpty()) {
                throw buildEpoxyException("Attributes cannot be empty")
            }
            if (defaultAttribute != null && defaultAttribute.codeToSetDefault.isEmpty &&
                !hasDefaultKotlinValue(defaultAttribute)
            ) {
                throw buildEpoxyException("Default attribute has no default code")
            }
            this.defaultAttribute = defaultAttribute
            isRequired = defaultAttribute == null
            name = groupName
            this.attributes =
                ArrayList(attributes)
        }
    }

    companion object {
        const val RESET_METHOD = "reset"
        const val GENERATED_CLASS_NAME_SUFFIX = "_"
        const val GENERATED_MODEL_SUFFIX = "Model$GENERATED_CLASS_NAME_SUFFIX"

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