elsa-workflows/elsa-core · error · InvalidOperationException

The memory block ' ' does not exist.

Error message

The memory block '{blockReference}' does not exist.

What it means

ActivityExecutionContext.Get(MemoryBlockReference) throws InvalidOperationException when the referenced memory block does not exist in the workflow's memory register. Memory blocks back variables, arguments, and outputs; requesting a block that was never registered (or was removed) fails fast instead of returning a misleading null.

Solutions

1. Ensure the variable/output is declared in a scope enclosing the activity calling Get, so its memory block is registered.
2. Compare the block reference Id in the message against declared variables/outputs in the definition.
3. Use context.TryGet(blockReference, out var value) when absence is an expected condition.
4. If resuming persisted instances, verify the memory store contains the block (persistence provider configured correctly).

Example fix

// before
var value = context.Get(myVariable); // throws if block absent
// after
if (context.TryGet(myVariable, out var value))
{
    // use value
}
else
{
    value = defaultValue;
}

// check the block exists before reading
if (context.TryGet(blockReference, out var existing))
{
    // safe to use existing
}

bool TryGetMemoryBlock(ActivityExecutionContext context, MemoryBlockReference reference, out object? value) => context.TryGet(reference, out value);

try { var value = context.Get(myVariable); }
catch (InvalidOperationException ex) when (ex.Message.Contains("does not exist"))
{
    logger.LogWarning(ex, "Memory block {Id} missing; using default", myVariable.Id);
    value = defaultValue;
}

When it happens

Trigger: Calling context.Get(someVariable) or context.Get(output) where the variable/output's MemoryBlockReference was never allocated — the variable is not declared in scope, the block belongs to a different scope, or the reference ID is stale.

Common situations: Reading an output of an activity that never executed (block not yet created); referencing a deleted/renamed variable; a child activity reading a sibling scope's variable; resuming an instance whose memory was not persisted/restored.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

• AlterationFaultCodes.PlanNotFound
• Activity type not found
• Variable ' ' not found.
• Workflow definition not found.
• Workflow instance not found.

AI-assisted analysis of elsa-workflows/elsa-core@fe9217bdfa (2026-09-13). Data as JSON: /api/errors/cc051d34f37d4d6a. Report an issue: GitHub.

Appendix: source

Thrown at src/modules/Elsa.Workflows.Core/Contexts/ActivityExecutionContext.cs:708

    public T? Get<T>(Output<T>? output) => output == null ? default : Get<T>(output.MemoryBlockReference());

    /// <summary>
    /// Gets the value of the specified output.
    /// </summary>
    /// <param name="output">The output.</param>
    /// <returns>The output value.</returns>
    public object? Get(Output? output) => output == null ? null : Get(output.MemoryBlockReference());

    /// <summary>
    /// Gets the value of the specified memory block.
    /// </summary>
    /// <param name="blockReference">The memory block reference.</param>
    /// <returns>The memory block value.</returns>
    /// <exception cref="InvalidOperationException">The memory block does not exist.</exception>
    public object? Get(MemoryBlockReference blockReference)
    {
        return !TryGet(blockReference, out var value)
            ? throw new InvalidOperationException($"The memory block '{blockReference}' does not exist.")
            : value;
    }

    /// <summary>
    /// Gets the value of the specified memory block.
    /// </summary>
    /// <param name="blockReference">The memory block reference.</param>
    /// <typeparam name="T">The type of the memory block.</typeparam>
    /// <returns>The memory block value.</returns>
    public T? Get<T>(MemoryBlockReference blockReference)
    {
        var value = Get(blockReference);
        return value != null ? value.ConvertTo<T>() : default;
    }

    /// <summary>
    /// Tries to get the value of the specified memory block.
    /// </summary>

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