flowable/flowable-engine · error · UnsupportedOperationException

Empty object, no variables can be removed

Error message

Empty object, no variables can be removed

What it means

Deliberate unsupported-operation sentinel: EmptyVariableScope is an immutable placeholder scope, so removeVariable (like all mutators) is hard-wired to throw; it fires only if code mutates the shared empty scope.

Solutions

1. Guard with instanceof EmptyVariableScope and skip the removal.
2. Fetch the live execution/task via runtimeService/taskService before removing.
3. Perform removals during the active delegate execution.
4. If nothing should remain, consider deleting the whole execution/instance instead of per-variable removal.

Example fix

// before
scope.removeVariable("tempData");

// after
if (!(scope instanceof EmptyVariableScope)) {
    scope.removeVariable("tempData");
}

if (scope instanceof EmptyVariableScope) {
    throw new IllegalStateException("Cannot remove variables from empty scope");
}

boolean isWritableScope(VariableScope scope) {
    return scope != null && !(scope instanceof EmptyVariableScope);
}

try {
    scope.removeVariable(name);
} catch (UnsupportedOperationException e) {
    if (e.getMessage() != null && e.getMessage().contains("Empty object")) {
        logger.warn("Removal skipped: empty scope");
    } else {
        throw e;
    }
}

When it happens

Trigger: Calling removeVariable(name) on EmptyVariableScope, e.g. cleanup code removing variables on a scope that resolved to the empty sentinel.

Common situations: Cleanup logic in delegates/listeners deleting variables after the process instance ended; generic variable-management helpers calling removeVariable on whatever scope they were handed.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• Empty object, no variables can be created
• Empty object, no variables can be set
• can't clear configuration beans
• can't search values in configuration beans
• Cannot change fixed value with

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/41d481a4e47be24b. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable-variable-service-api/src/main/java/org/flowable/variable/api/delegate/EmptyVariableScope.java:210

        return false;
    }

    @Override
    public boolean hasVariableLocal(String variableName) {
        return false;
    }

    public void createVariableLocal(String variableName, Object value) {
        throw new UnsupportedOperationException("Empty object, no variables can be created");
    }

    public void createVariablesLocal(Map<String, ? extends Object> variables) {
        throw new UnsupportedOperationException("Empty object, no variables can be created");
    }

    @Override
    public void removeVariable(String variableName) {
        throw new UnsupportedOperationException("Empty object, no variables can be removed");
    }

    @Override
    public void removeVariableLocal(String variableName) {
        throw new UnsupportedOperationException("Empty object, no variables can be removed");
    }

    @Override
    public void removeVariables() {
        throw new UnsupportedOperationException("Empty object, no variables can be removed");
    }

    @Override
    public void removeVariablesLocal() {
        throw new UnsupportedOperationException("Empty object, no variables can be removed");
    }

    @Override

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