presto-main/src/main/java/io/prestosql/metadata/SpecializedFunctionKey.java/SpecializedFunctionKey/SpecializedFunctionKey
class SpecializedFunctionKey:    public SpecializedFunctionKey(SqlFunction function, BoundVariables boundVariables, int arity)
    {
        this.function = requireNonNull(function, "function is null");
        this.boundVariables = requireNonNull(boundVariables, "boundVariables is null");
        this.arity = arity;
    }