litedb-org/LiteDB · error · ArgumentNullException

field

Error message

field

What it means

Query.EQ(string field, BsonValue value) builds a BsonExpression of the form '$field = $value' for an equality filter. At Query.cs:59 it throws ArgumentNullException(nameof(field)) whenever field is null, empty, or whitespace, because such a value cannot be interpolated into a valid BsonExpression and would later fail at parse time with a confusing error. LiteDB fails fast on the public API surface so the caller sees the real cause. The check uses IsNullOrWhiteSpace, so a string of spaces is treated the same as null.

Source

Thrown at LiteDB/Client/Structures/Query.cs:59

            return query;
        }

        /// <summary>
        /// Returns all documents
        /// </summary>
        public static Query All(string field, int order = Ascending)
        {
            var query = new Query();
            query.OrderBy.Add(new QueryOrder(BsonExpression.Create(field), order));
            return query;
        }

        /// <summary>
        /// Returns all documents that value are equals to value (=)
        /// </summary>
        public static BsonExpression EQ(string field, BsonValue value)
        {
            if (field.IsNullOrWhiteSpace()) throw new ArgumentNullException(nameof(field));

            return BsonExpression.Create($"{field} = {value ?? BsonValue.Null}");
        }

        /// <summary>
        /// Returns all documents that value are less than value (&lt;)
        /// </summary>
        public static BsonExpression LT(string field, BsonValue value)
        {
            if (field.IsNullOrWhiteSpace()) throw new ArgumentNullException(nameof(field));

            return BsonExpression.Create($"{field} < {value ?? BsonValue.Null}");
        }

        /// <summary>
        /// Returns all documents that value are less than or equals value (&lt;=)
        /// </summary>
        public static BsonExpression LTE(string field, BsonValue value)

View on GitHub (pinned to f906a5f850)

Solutions

1. Pass a concrete non-empty document field path such as Query.EQ("_id", id).
2. Guard the variable first: if (name.IsNullOrWhiteSpace()) return; before calling Query.EQ.
3. Centralize field names in constants so they can never silently become empty.

Example fix

// before
var q = Query.EQ(fieldName, age); // fieldName may be null/empty

// after
if (string.IsNullOrWhiteSpace(fieldName))
    throw new InvalidOperationException("fieldName must be supplied by the caller.");
var q = Query.EQ(fieldName, age);

if (string.IsNullOrWhiteSpace(field))
    throw new ArgumentException("Field name is required.", nameof(field));
var q = Query.EQ(field, value);

static bool IsValidField(string field) => !string.IsNullOrWhiteSpace(field);

When it happens

Trigger: Calling Query.EQ(null, 1), Query.EQ("", 1), or Query.EQ(" ", 1). Also when the field name is loaded from configuration, a dictionary lookup, or JSON deserialization that yields null/empty.

Common situations: Field name read from appsettings or an environment variable that was not set; a property name built dynamically (e.g. char-by-char or via a loop) that produced an empty string; a refactor that swapped argument order and passed the value where the field belongs.

Related errors

• Value cannot be null. (Parameter 'field')
• Value cannot be null. (Parameter 'arrayField')
• Value cannot be null. (Parameter 'left')
• At least two Query should be passed
• command

AI-assisted analysis of litedb-org/LiteDB@f906a5f850 (2026-08-13). Data as JSON: /api/errors/c9353cc7a882efed. Report an issue: GitHub.