presto-main/src/main/java/io/prestosql/operator/aggregation/state/StateCompiler.java/StateCompiler/initialValueExpression
class StateCompiler:        public BytecodeExpression initialValueExpression()
        {
            if (initialValue == null) {
                return defaultValue(type);
            }
            if (initialValue instanceof Number) {
                return constantNumber((Number) initialValue);
            }
            else if (initialValue instanceof Boolean) {
                return constantBoolean((boolean) initialValue);
            }
            else {
                throw new IllegalArgumentException("Unsupported initial value type: " + initialValue.getClass());
            }
        }