java.lang.NullPointerException at jdk.compiler/com.sun.tools.javac.comp.Flow

ADDITIONAL SYSTEM INFORMATION :
java compiler 11.0.11

A DESCRIPTION OF THE PROBLEM :
NPE while compiling code with empty diamond to infer generic type. See the code provided

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
compile the code

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
compiles and infers the type from the function argument
ACTUAL -
doesnt compile, NPE

---------- BEGIN SOURCE ----------
import com.google.common.reflect.TypeToken;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

import java.math.BigDecimal;
import java.util.Map;

public class Test {

    private static final Gson GSON = new GsonBuilder().create();

    public void testFunc() {
        testFunc2(fromMongoJsonObject(new TypeToken<>() {
        }));
    }

    void testFunc2(Map<Long, BigDecimal> aMap) {
    }

    private static <R> R fromMongoJsonObject(TypeToken<R> aTypeToken) {
        return GSON.fromJson("Test", aTypeToken.getType());
    }
}

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

CUSTOMER SUBMITTED WORKAROUND :
Specify the generic explicitly in diamond:

import com.google.common.reflect.TypeToken;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;

import java.math.BigDecimal;
import java.util.Map;

public class Test {

    private static final Gson GSON = new GsonBuilder().create();

    public void testFunc() {
        testFunc2(fromMongoJsonObject(new TypeToken<Map<Long, BigDecimal>>() {
        }));
    }

    void testFunc2(Map<Long, BigDecimal> aMap) {
    }

    private static <R> R fromMongoJsonObject(TypeToken<R> aTypeToken) {
        return GSON.fromJson("Test", aTypeToken.getType());
    }
}


FREQUENCY : always