FULL PRODUCT VERSION :
java version "1.8.0_60"
Java(TM) SE Runtime Environment (build 1.8.0_60-b27)
Java HotSpot(TM) 64-Bit Server VM (build 25.60-b23, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 6.1.7601]

A DESCRIPTION OF THE PROBLEM :
At runtime I get a java.lang.BootstrapMethodError which is caused by a java.lang.invoke.LambdaConversionException

Basically, I have a type T extends Enum<T> & Supplier<K>
and then use a method reference which refers to the Supplier's "get" method, i.e. T::get

Note: since this error occurs at run-time & involves java.lang.invoke, I filed the issue against java.lang, but it may well be that the actual issue is in the compiler.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile and execute the attached test case

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
A single line of output
ACTUAL -
An exception is thrown

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------

import java.time.LocalDate;
import java.util.EnumSet;
import java.util.Objects;
import java.util.Optional;
import java.util.function.Function;
import java.util.function.Supplier;

public class Issue {

	public static void main(String[] args) {
		System.out.println(valueOfKey(Size.class, LocalDate.now()));
	}

	enum Size implements Supplier<LocalDate> {
		S, M, L;

		@Override
		public LocalDate get() {
			return LocalDate.now();
		}

	}

	public static <K, T extends Enum<T> & Supplier<K>> Optional<T> valueOfKey(Class<T> enumType, K key) {
		return valueOf(enumType, key, T::get);
	}

	public static <K, T extends Enum<T>> Optional<T> valueOf(Class<T> enumType, K key, Function<T, K> keyExtractor) {
		return EnumSet.allOf(enumType)
				.stream()
				.filter(t -> Objects.equals(keyExtractor.apply(t), key))
				.findFirst();
	}

}

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