javac bug. java8u20 compiler cannot compile this code. but eclipse4.4.0 compiler can compile.

error.log

src\example\Main.java:13: error: reference to of is ambiguous
		Consumers.of(Main::exec);
		         ^
  both method of(OutputStreamConsumer) in Consumers and method of(WriterConsumer) in Consumers match
src\example\Main.java:13: error: method of in interface Consumers cannot be applied to given types;
		Consumers.of(Main::exec);
		            ^
  required: OutputStreamConsumer
  found: Main::exec
  reason: argument mismatch; invalid method reference
      no suitable method found for exec(Object,OutputStream)
          method Main.exec(Object) is not applicable
            (actual and formal argument lists differ in length)
          method Main.exec(Object,Appendable) is not applicable
            (argument mismatch; OutputStream cannot be converted to Appendable)
2 errors

Main.java

import java.io.OutputStream;
import java.io.Writer;

public class Main {
	
	public static String exec(Object value) { return null; }
	
	public static void exec(Object value, Appendable appendable) {}
	
	public static void main(String[] args) {
		Consumers.of(Main::exec);
	}
	
	public interface Consumers {
		public static void of(OutputStreamConsumer fn) {}
		public static void of(WriterConsumer fn) {}
		
		public interface OutputStreamConsumer {
			void render(Object model, OutputStream out);
		}
		public interface WriterConsumer {
			void render(Object model, Writer out);
		}
	}
}