presto-main/src/main/java/io/prestosql/metadata/PolymorphicScalarFunctionBuilder.java/PolymorphicScalarFunctionBuilder/signature
class PolymorphicScalarFunctionBuilder:    public PolymorphicScalarFunctionBuilder signature(Signature signature)
    {
        this.signature = requireNonNull(signature, "signature is null");
        this.hidden = Optional.of(hidden.orElse(isOperator(signature)));
        return this;
    }