presto-main/src/main/java/io/prestosql/metadata/SessionPropertyManager.java/SessionPropertyManager/getMapKeyType
class SessionPropertyManager:    private static Class<?> getMapKeyType(Type type)
    {
        if (VarcharType.VARCHAR.equals(type)) {
            return String.class;
        }
        if (BooleanType.BOOLEAN.equals(type)) {
            return Boolean.class;
        }
        if (BigintType.BIGINT.equals(type)) {
            return Long.class;
        }
        if (IntegerType.INTEGER.equals(type)) {
            return Integer.class;
        }
        if (DoubleType.DOUBLE.equals(type)) {
            return Double.class;
        }
        throw new PrestoException(INVALID_SESSION_PROPERTY, format("Session property map key type %s is not supported", type));
    }