@SuppressWarnings("unchecked")
    public <T> Map<String, T> getMap(String attrName) {
        return (Map<String, T>)attributes.get(attrName);
    }
Returns the value of the specified attribute in the current item as a map
of string-to-<code>T</code>'s; or null if the attribute either doesn't
exist or the attribute value is null. Note that any numeric type of a
map is always canonicalized into <code>BigDecimal</code>, and therefore
if <code>T</code> referred to a <code>Number</code> type, it would need
to be <code>BigDecimal</code> to avoid a class cast exception.

@see #isNull(String) #isNull(String) to check if the attribute value is
     null.
@see #isPresent(String) #isPresent(String) to check if the attribute
     value is present.

@throws ClassCastException
            if the attribute is not a map of string to <code>T</code>
aws-java-sdk-dynamodb/src/main/java/com/amazonaws/services/dynamodbv2/document/Item.java