Error when neutral is null and exprs is empty in OperatorAST

[Seb35]

In SQLDSL, some methods like sum create an OperatorAST with a neutral argument (4th parameter) null, but in some cases (when exprs is empty) OperatorAST calls this.neutral.writeTo(b); so I guess it can create errors, something like:

AST tree = select(sum(), from(id("songs")));

because in OperatorAST in method writeTo, if this.neutral is null there is no method writeTo():

if (n == 0) {
	this.neutral.writeTo(b);
}

Obviously this would lead to incorrect SQL, so a choice must be taken: either throw an exception either write wrong SQL and let the SQL library trigger an error. Personally I would choose the second option because the objective of this library sqltrees is probably not to re-implement the whole (dialects of) SQL semantics.

I’m not completely affirmative because I’m not fluent in Java, so perhaps I miss some language detail. But I was interested by the article in MISC and I took as an exercice to transpile/implement it to PHP (I master this language), and in the corresponding situation PHP complains.