code: @CanIgnoreReturnValue
    @NonNullDecl
    public static <T extends Object> T checkNotNull(@NonNullDecl T reference) {
      if (reference == null) {
        throw new NullPointerException();
      }
      return reference;
    }
docs: Ensures that an object reference passed as a parameter to the calling method is not null.
  
  @param reference an object reference
  @return the non-null reference that was validated
  @throws NullPointerException if {@code reference} is null
  @see Verify#verifyNotNull Verify.verifyNotNull()