EmptyFieldStream.java

  Observable<Boolean> emptyFieldStream = Observable.combineLatest(
          RxTextView.textChanges(etEmail)
                  .map(new Func1<CharSequence, Boolean>() {
                      @Override
                      public Boolean call(CharSequence charSequence) {
                          return TextUtils.isEmpty(charSequence);
                      }
                  }),
          RxTextView.textChanges(etPassword)
                  .map(new Func1<CharSequence, Boolean>() {
                      @Override
                      public Boolean call(CharSequence charSequence) {
                          return TextUtils.isEmpty(charSequence);
                      }
                  }),
          RxTextView.textChanges(etPasswordConfirmation)
                  .map(new Func1<CharSequence, Boolean>() {
                      @Override
                      public Boolean call(CharSequence charSequence) {
                          return TextUtils.isEmpty(charSequence);
                      }
                  }),
          new Func3<Boolean, Boolean, Boolean, Boolean>() {
              @Override
              public Boolean call(Boolean emailEmpty, Boolean passwordEmpty, Boolean passwordConfirmationEmpty) {
                  return emailEmpty || passwordEmpty || passwordConfirmationEmpty;
              }
          }
  );