DynamoDB Set of Objects Insert and Get - amazon-dynamodb

Question

I have the following DynamoDB Table
#Builder
#DynamoDBTable(tableName = "rule_templates")
#Setter
#NoArgsConstructor
#AllArgsConstructor
public class DynamoRuleTemplate {
private String id;
private DataType dataType;
private String displayName;
private String helpText;
private String expression;
private Set<Param> params;
#DynamoDBHashKey(attributeName = "id")
public String getId() {
return id;
}
#DynamoDBAttribute(attributeName = "data_type")
public DataType getDataType() {
return dataType;
}
#DynamoDBAttribute(attributeName = "display_name")
public String getDisplayName() {
return displayName;
}
#DynamoDBAttribute(attributeName = "help_text")
public String getHelpText() {
return helpText;
}
#DynamoDBAttribute(attributeName = "expression")
public String getExpression() {
return expression;
}
#DynamoDBTypeConverted(converter = ParamSet.class)
#DynamoDBAttribute(attributeName = "params")
public Set<Param> getParams() {
return params;
}
}
Here is the Param class:
#Data
public class Param {
private DataType dataType;
private String identifier;
private String displayName;
private String helpText;
}
I am pre-filling the table with some data in the form of json through AWS CLI like:
{
"id": {
"S": "string-length-range"
},
"data_type": {
"S": "STRING"
},
"display_name": {
"S": "String length range"
},
"expression": {
"S": "$val.length() <= $max && $val.length() >= $min"
},
"help_text": {
"S": "String length range"
},
"params": {
"L": [
{
"M": {
"dataType": {
"S": "INTEGER"
},
"displayName": {
"S": "max"
},
"identifier": {
"S": "$max"
}
}
},
{
"M": {
"dataType": {
"S": "INTEGER"
},
"displayName": {
"S": "min"
},
"identifier": {
"S": "$min"
}
}
}
]
}
}
But while doing a GET from the table using JAVA application, I'm getting the following error for params field: com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMappingException: expected S in value {L: [{M: {identifier={S: $max,}, displayName={S: max,}, dataType={S: INTEGER,}},}, {M: {identifier={S: $min,}, displayName={S: min,}, dataType={S: INTEGER,}, rule={M: {expression={S: $min >= 0,}},}},}],}
Can someone help me with the correct json so that I don't get the above error?