ADDITIONAL SYSTEM INFORMATION :
Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.8+10-LTS, mixed mode)

A DESCRIPTION OF THE PROBLEM :
A regression occurred when I migrated my code from java 8 to java 11, and javac 11 compiler report an error now systematically
 

REGRESSION : Last worked in version 8

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
compiling project with a javac 11. 

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
compiler must infer correct lambda return type and throws exception without errors
ACTUAL -
unreported exception IOException; must be caught or declared to be thrown
                .map(Lambda.function(resource -> Mapper.toString(resource),
                                                                ^
1 error

---------- BEGIN SOURCE ----------
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
import java.util.function.BiFunction;
import java.util.function.Function;

class BugGenericSneakyThrowInference {
    public static void main(String[] args) {
        process(new ArrayList<>());
    }

    public static String[] process(List<Resource> resources) {

        return resources.stream()
                .map(Lambda.function(resource -> Mapper.toString(resource),
                        (res, ex) -> Lambda.sneakyThrow(ex)))
                .toArray(String[]::new);

    }
}

interface Resource {

    InputStream getInputStream() throws IOException;
}

interface Function1<T, R> extends Function<T, R> {

    interface WithException<T, R, E extends Throwable> {

        R apply(T t) throws E;

        default Function1<T, R> cast(BiFunction<T, Throwable, R> fn) {
            return t -> {
                try {
                    return apply(t);
                } catch (Throwable e) {
                    return fn.apply(t, e);
                }
            };
        }
    }
}

final class Lambda {

    public static <T, R, E extends Throwable> Function<T, R> function(Function1.WithException<T, R, E> function,
            BiFunction<T, Throwable, R> errorFn) {
        return function.cast(errorFn);
    }

    @SuppressWarnings("unchecked")
    public static <R, E extends Throwable> R sneakyThrow(Throwable e) throws E {
        throw (E) e;
    }

}

class Mapper {

    static String toString(Resource resource) throws IOException {
        return resource.getInputStream().toString();
    }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
public static String[] process(List<Resource> resources) {
        return resources.stream()
                .map(Lambda.function((Function1.WithException<Resource, String, IOException>)(resource -> Mapper.toString(resource)),
                        (res, ex) -> Lambda.sneakyThrow(ex)))
                .toArray(String[]::new);

    }

FREQUENCY : always