After the recent changes to lowering of lambdas, javac is generating unnecessary boxing conversions for expression bodied lambdas that implement a void returning method.

class T {
  int g() { return 0; }
  Runnable r = () -> g();
}

Before:

  private void lambda$new$0();
    descriptor: ()V
    flags: (0x1002) ACC_PRIVATE, ACC_SYNTHETIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: invokevirtual #17 // Method g:()I
         4: pop
         5: return
      LineNumberTable:
        line 3: 0

After:

  private void lambda$new$0();
    descriptor: ()V
    flags: (0x1002) ACC_PRIVATE, ACC_SYNTHETIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: invokevirtual #17 // Method g:()I
         4: invokestatic #21 // Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
         7: pop
         8: return
      LineNumberTable:
        line 3: 0

Note the new call to Integer.valueOf

javac is not an optimizing compiler, but the new calls are unnecessary can result in additional allocations, and would be nice to omit.