Error: dynamodb does not support null values

DynamoDB supports the NULL attribute type. A message saying null values are unsupported usually concerns a key, a client mapper or an incorrectly serialized request, not a blanket service restriction.

// DynamoDBDocumentClient native value:
const item = { pk: "record-1", optionalNote: null };

// Equivalent low-level AttributeValue map:
const rawItem = { pk: { S: "record-1" }, optionalNote: { NULL: true } };

With boto3 resource methods, Python None maps to NULL. A missing attribute is different: omit it on a put, or REMOVE it in an update. A NULL attribute still exists for attribute_exists checks.

Primary-key attributes must have valid scalar values. Optional GSI keys can be absent for sparse indexing, but cannot be NULL when present. Do not change a key schema to permit NULL; that is not supported. Empty non-key strings and binary values are a separate feature, and empty sets remain invalid. Check mapper-specific null handling if your SDK omits or removes null properties.

See data types and AWS documentation.