ConditionalExpr resolves to wrong type

[kgeilmann]

The type solver always resolves conditional expressions to the type of the then part, which makes e.g. s == null ? null : s.toString() surprisingly being resolved to the null type instead of String.

[ftomassetti]

The current implementation is wrong and the rules for implementing it correctly are far from trivial. There is a pretty significant part of the JLS discussing about this: https://docs.oracle.com/javase/specs/jls/se10/html/jls-15.html#jls-15.25

[jlerbsc]

Reference conditional expression refer to #2978

[jlerbsc]

This issue is resolved but we have to manage case of conditional reference expression and poly expression.

[jlerbsc]

Poly expression is resolved with PR #2994

[jlerbsc]

TODO manage lub function (in TypeHelper.leastUpperBound) and update TypeExtractor.visit(ConditionalExpr node, Boolean solveLambdas) to manage reference conditional expression.

[jlerbsc]

Resolved in PR #3880