What causes "Can not convert {0} to Char." in JamesNK/Newtonsoft.Json?

Check token.Type is String or Integer before the cast; remember Boolean is rejected even though it is accepted by number casts.

JamesNK/Newtonsoft.Json · error · ArgumentException

Can not convert {0} to Char.

Error message

Can not convert {0} to Char.

What it means

Thrown by the explicit nullable cast operator char?(JToken?) at JToken.cs:792. The valid type set is CharTypes = {Integer, Float, String, Comment, Raw} — note Boolean is NOT included (unlike NumberTypes). With nullable:true, JSON null/undefined pass. The error fires for Boolean, Date, Guid, Uri, Bytes, Object, Array, or any non-JValue token.

Source

Thrown at Src/Newtonsoft.Json/Linq/JToken.cs:792

            return (v.Value != null) ? (double?)Convert.ToDouble(v.Value, CultureInfo.InvariantCulture) : null;
        }

        /// <summary>
        /// Performs an explicit conversion from <see cref="JToken"/> to <see cref="Nullable{T}"/> of <see cref="Char"/>.
        /// </summary>
        /// <param name="value">The value.</param>
        /// <returns>The result of the conversion.</returns>
        public static explicit operator char?(JToken? value)
        {
            if (value == null)
            {
                return null;
            }

            JValue? v = EnsureValue(value);
            if (v == null || !ValidateToken(v, CharTypes, true))
            {
                throw new ArgumentException("Can not convert {0} to Char.".FormatWith(CultureInfo.InvariantCulture, GetType(value)));
            }

#if HAVE_BIG_INTEGER
            if (v.Value is BigInteger integer)
            {
                return (char?)integer;
            }
#endif

            return (v.Value != null) ? (char?)Convert.ToChar(v.Value, CultureInfo.InvariantCulture) : null;
        }

        /// <summary>
        /// Performs an explicit conversion from <see cref="JToken"/> to <see cref="Int32"/>.
        /// </summary>
        /// <param name="value">The value.</param>
        /// <returns>The result of the conversion.</returns>
        public static explicit operator int(JToken value)

View on GitHub (pinned to 4f73e74372)

Solutions

Check token.Type is String or Integer before the cast; remember Boolean is rejected even though it is accepted by number casts.
Use token.Value<char?>() to get default for incompatible tokens.
Validate the field is a 1-character string scalar in the JSON.
Deserialize into a nullable char POCO property.

Example fix

// before
char? c = (char?)token["initial"]; // throws when initial is a boolean

// after
char? c = (token["initial"]?.Type is JTokenType.String)
    ? (char?)token["initial"]
    : null;

Defensive patterns

Strategy: type-guard

Validate before calling

// Verify the token is a char-compatible scalar (CharTypes excludes Boolean; nullable tolerates JSON null)
static bool CanToNullableChar(JToken? t) =>
    t is not JValue v || v.Type is JTokenType.Integer or JTokenType.Float
        or JTokenType.String or JTokenType.Null or JTokenType.Undefined;

Type guard

static char? SafeChar(JToken? t) => t switch {
    JValue v when v.Type is JTokenType.Integer or JTokenType.Float
                       or JTokenType.String => (char?)t,
    JValue v when v.Type is JTokenType.Null or JTokenType.Undefined => null,
    _ => null // Boolean, Date, container, etc.
};

Try / catch

try
{
    char? c = (char?)token;
}
catch (ArgumentException ex) when (ex.Message.StartsWith("Can not convert"))
{
    // token is Boolean/Date/container; default to null
}

Prevention

Remember char casts reject Boolean even though number casts accept it.
Check token.Type is String or Integer before casting.
Use token.Value<char?>() for tolerant default handling.
Deserialize into a nullable char POCO property.

When it happens

Trigger: Casting a Boolean JValue (true/false) to (char?)token; casting a Date/Guid/Uri or a JObject/JArray to char?. A JSON null returns null.

Common situations: A single-character field represented as a JSON boolean; a char field that became an object/array; reading a Guid/Uri as a char.

Related errors

AI-assisted analysis of JamesNK/Newtonsoft.Json@4f73e74372 (2026-08-07). Data as JSON: /api/errors/f3db26a43d59e358. Report an issue: GitHub.