elsa-workflows/elsa-core · error · JsonException

Expected number or string.

Error message

Expected number or string.

What it means

BigIntegerJsonConverter.Read deserializes a JSON token into a BigInteger, accepting only JSON numbers and strings parseable as long. Any other token type (true, false, null, object, array, etc.) causes a JsonException with the message 'Expected number or string.'

Solutions

1. Fix the JSON payload so the field is a number or a numeric string.
2. Make the property nullable or use JsonIgnoreCondition so nulls bypass the converter.
3. Use a custom converter override (or Read handling JsonTokenType.Null) if null must be accepted.
4. Verify the converter is only applied to properties that are actually numeric.

Example fix

// before
{"count": null}
// after
{"count": 42}

if (token.Type is not (JsonTokenType.Number or JsonTokenType.String))
    throw new JsonException($"Expected number or string for BigInteger, got {token.Type}.");

bool IsBigIntegerToken(JsonTokenType t) => t is JsonTokenType.Number or JsonTokenType.String;

try { var value = JsonSerializer.Deserialize<BigInteger>(json, options); }
catch (JsonException ex) { log.LogWarning(ex, "Invalid BigInteger payload"); value = BigInteger.Zero; }

When it happens

Trigger: Deserializing JSON where a field bound to BigInteger holds a non-numeric, non-string token — e.g. true/false/null, a nested object, or an array.

Common situations: API responses returning null for a numeric field; payload shape changes upstream; wiring the converter onto a bool or object property by mistake.

Understand the failure class

Background: "failed to unmarshal" / json.Unmarshal errors: why parsing a response into a Go struct fails and how to fix it — this error's family across 23 libraries.

Related errors

• Cannot convert to bool
• Expected an EndObject token
• Cannot deserialize to .
• Failed to deserialize
• The binding to activity type

AI-assisted analysis of elsa-workflows/elsa-core@fe9217bdfa (2026-09-13). Data as JSON: /api/errors/09bad3a4f37922fb. Report an issue: GitHub.

Appendix: source

Thrown at src/modules/Elsa.Common/Converters/BigIntegerJsonConverter.cs:24

/// <summary>
/// Converts big integers to and from JSON strings.
/// </summary>
public class BigIntegerJsonConverter : JsonConverter<BigInteger>
{
    /// <inheritdoc />
    public override BigInteger Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        if (reader.TokenType == JsonTokenType.Number)
            return reader.GetInt64();

        if (reader.TokenType == JsonTokenType.String)
        {
            var value = reader.GetString()!;
            return long.Parse(value);
        }

        throw new JsonException("Expected number or string.");
    }

    /// <inheritdoc />
    public override void Write(Utf8JsonWriter writer, BigInteger value, JsonSerializerOptions options)
    {
        // Write the Big Integer as a JSON number.
        writer.WriteNumberValue((long)value);
    }
}

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