code: /*
   * Copyright (c) 2016-present, RxJava Contributors.
   *
   * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
   * compliance with the License. You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software distributed under the License is
   * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
   * the License for the specific language governing permissions and limitations under the License.
   */
  
  package io.reactivex.rxjava3.internal.operators.maybe;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.exceptions.Exceptions;
  import io.reactivex.rxjava3.internal.disposables.EmptyDisposable;
  
  import java.util.Objects;
  
  /**
   * Calls a MaybeOperator for the incoming MaybeObserver.
   *
   * @param <T> the upstream value type
   * @param <R> the downstream value type
   */
  public final class MaybeLift<T, R> extends AbstractMaybeWithUpstream<T, R> {
  
      final MaybeOperator<? extends R, ? super T> operator;
  
      public MaybeLift(MaybeSource<T> source, MaybeOperator<? extends R, ? super T> operator) {
          super(source);
          this.operator = operator;
      }
  
      @Override
      protected void subscribeActual(MaybeObserver<? super R> observer) {
          MaybeObserver<? super T> lifted;
  
          try {
              lifted = Objects.requireNonNull(operator.apply(observer), "The operator returned a null MaybeObserver");
          } catch (Throwable ex) {
              Exceptions.throwIfFatal(ex);
              EmptyDisposable.error(ex, observer);
              return;
          }
  
          source.subscribe(lifted);
      }
  }
  