解决JAVA8 Collectors.toMap value为null报错的问题

Caused by: java.lang.NullPointerException
 java.util.HashMap.merge(HashMap.java:1224)
 java.util.stream.Collectors.lambda$toMap$58(Collectors.java:1320)
 java.util.stream.ReduceOps$3ReducingSink.accept(ReduceOps.java:169)
 java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1374)
 java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
 java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
 java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)

default V merge(K key, V value,
  BiFunction<? super V, ? super V, ? extends V> remappingFunction) {
 Objects.requireNonNull(remappingFunction);
 //在这里判断了value不可为null
 Objects.requireNonNull(value);
 V oldValue = get(key);
 V newValue = (oldValue == null) ? value :
   remappingFunction.apply(oldValue, value);
 if(newValue == null) {
  remove(key);
 } else {
  put(key, newValue);
 }
 return newValue;
 }

Map<String,Integer> videoGiftSumVoMap=videoGiftSum.stream().collect(Collectors.toMap
(callRecodVo -> Optional.ofNullable(callRecodVo).map
(CallRecodVo::getStatdate).orElse(0),callRecodVo -> Optional.ofNullable(callRecodVo).map
(CallRecodVo::getVideogiftdiamond).orElse(0), (key1, key2) -> key2));