public ScanSpec withValueMap(Map<String, Object> valueMap) {
        if (valueMap == null)
            this.valueMap = null;
        else
            this.valueMap = Collections.unmodifiableMap(new LinkedHashMap<String, Object>(valueMap));
        return this;
    }
Applicable only when an expression has been specified. Used to
specify the actual values for the attribute-value placeholders.

@see ScanRequest#withExpressionAttributeValues(Map)
aws-java-sdk-dynamodb/src/main/java/com/amazonaws/services/dynamodbv2/document/spec/ScanSpec.java