Code compiles in java8 but not in java9 : "incompatible types: java.lang.Object cannot be converted ..."

FULL PRODUCT VERSION :
java version "9.0.4"
Java(TM) SE Runtime Environment (build 9.0.4+11)
Java HotSpot(TM) 64-Bit Server VM (build 9.0.4+11, mixed mode)


ADDITIONAL OS VERSION INFORMATION :
Windows 10 Enterprise 64-bit

A DESCRIPTION OF THE PROBLEM :
The attached code does not compile in java 9, intellij idea do not suggest any problems with it. To make it compiling one must do a implicit cast or assign intermediate result to a typed variable.


REGRESSION. Last worked in version 8u161

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Try to compile the attached code in java 9

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
it compiles since it is compilable in java 8 ant development tool (intellij idea) do not report any problems with the code.
ACTUAL -
Error:(20, 113) java: incompatible types: java.lang.Object cannot be converted to /package name here/.Base

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Error:(20, 113) java: incompatible types: java.lang.Object cannot be converted to /package name here/.Base

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
public class StreamOfStreams {


  public static void main(String[] args) {
    Helper h = new Helper();
    Stream.of(h.get(A.class).stream(), h.get(B.class).stream()).flatMap(Function.identity()).filter(r -> h.test(r));
  }
}

class Base {
}

class A extends Base {
}

class B extends Base {
}

class Helper {
  public <T extends Base> Set<T> get(final Class<T> clazz) {
    return new HashSet<>();
  }

  public boolean test(Base b) {
    return true;
  }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
public class StreamOfStreams {


  public static void main(String[] args) {
    Helper h = new Helper();
    Stream.of(h.get(A.class).stream(), h.get(B.class).stream()).flatMap(Function.identity()).filter(r -> h.test((Base)r));
  }
}

class Base {
}

class A extends Base {
}

class B extends Base {
}

class Helper {
  public <T extends Base> Set<T> get(final Class<T> clazz) {
    return new HashSet<>();
  }

  public boolean test(Base b) {
    return true;
  }
}