title: readString can only be called when CurrentBSONType is STRING, not when CurrentBSONType is OBJECT_ID
body: <p>I get the following error - while reading a POJO, I am able to insert / update and delete successfully.</p>
  
  <p>We are using mongodb-driver-reactivestreams (1.9.0)</p>
  
  <pre><code>org.bson.codecs.configuration.CodecConfigurationException: An exception occurred when decoding using the AutomaticPojoCodec.
  Decoding into a 'FooBar' failed with the following exception:
  
  Failed to decode 'FooBar'. Decoding '_id' errored with: readString can only be called when CurrentBSONType is STRING, not when CurrentBSONType is OBJECT_ID.
  
  A custom Codec or PojoCodec may need to be explicitly configured and registered to handle this type.
      at org.bson.codecs.pojo.AutomaticPojoCodec.decode(AutomaticPojoCodec.java:40) ~[bson-3.7.1.jar:?]
      at com.mongodb.operation.CommandResultArrayCodec.decode(CommandResultArrayCodec.java:52) ~[mongodb-driver-core-3.8.0.jar:?]
      at com.mongodb.operation.CommandResultDocumentCodec.readValue(CommandResultDocumentCodec.java:60) ~[mongodb-driver-core-3.8.0.jar:?]
      at org.bson.codecs.BsonDocumentCodec.decode(BsonDocumentCodec.java:84) ~[bson-3.7.1.jar:?]
      at org.bson.codecs.BsonDocumentCodec.decode(BsonDocumentCodec.java:41) ~[bson-3.7.1.jar:?]
      at org.bson.codecs.configuration.LazyCodec.decode(LazyCodec.java:47) ~[bson-3.7.1.jar:?]
      at org.bson.codecs.BsonDocumentCodec.readValue(BsonDocumentCodec.java:101) ~[bson-3.7.1.jar:?]
      at com.mongodb.operation.CommandResultDocumentCodec.readValue(CommandResultDocumentCodec.java:63) ~[mongodb-driver-core-3.8.0.jar:?]
      at org.bson.codecs.BsonDocumentCodec.decode(BsonDocumentCodec.java:84) ~[bson-3.7.1.jar:?]
      at 
  
  Caused by: org.bson.codecs.configuration.CodecConfigurationException: Failed to decode 'FooBar'. Decoding '_id' errored with: readString can only be called when CurrentBSONType is STRING, not when CurrentBSONType is OBJECT_ID.
      at org.bson.codecs.pojo.PojoCodecImpl.decodePropertyModel(PojoCodecImpl.java:195) ~[bson-3.7.1.jar:?]
      at org.bson.codecs.pojo.PojoCodecImpl.decodeProperties(PojoCodecImpl.java:173) ~[bson-3.7.1.jar:?]
      at org.bson.codecs.pojo.PojoCodecImpl.decode(PojoCodecImpl.java:127) ~[bson-3.7.1.jar:?]
      at org.bson.codecs.pojo.PojoCodecImpl.decode(PojoCodecImpl.java:131) ~[bson-3.7.1.jar:?]
      at org.bson.codecs.pojo.AutomaticPojoCodec.decode(AutomaticPojoCodec.java:37) ~[bson-3.7.1.jar:?]
      ... 46 more
  Caused by: org.bson.BsonInvalidOperationException: readString can only be called when CurrentBSONType is STRING, not when CurrentBSONType is OBJECT_ID.
      at org.bson.AbstractBsonReader.verifyBSONType(AbstractBsonReader.java:690) ~[bson-3.7.1.jar:?]
      at org.bson.AbstractBsonReader.checkPreconditions(AbstractBsonReader.java:722) ~[bson-3.7.1.jar:?]
      at org.bson.AbstractBsonReader.readString(AbstractBsonReader.java:457) ~[bson-3.7.1.jar:?]
      at org.bson.codecs.StringCodec.decode(StringCodec.java:39) ~[bson-3.7.1.jar:?]
      at org.bson.codecs.StringCodec.decode(StringCodec.java:28) ~[bson-3.7.1.jar:?]
      at org.bson.codecs.DecoderContext.decodeWithChildContext(DecoderContext.java:93) ~[bson-3.7.1.jar:?]
      at org.bson.codecs.pojo.PojoCodecImpl.decodePropertyModel(PojoCodecImpl.java:189) ~[bson-3.7.1.jar:?]
      at org.bson.codecs.pojo.PojoCodecImpl.decodeProperties(PojoCodecImpl.java:173) ~[bson-3.7.1.jar:?]
      at org.bson.codecs.pojo.PojoCodecImpl.decode(PojoCodecImpl.java:127) ~[bson-3.7.1.jar:?]
      at org.bson.codecs.pojo.PojoCodecImpl.decode(PojoCodecImpl.java:131) ~[bson-3.7.1.jar:?]
      at org.bson.codecs.pojo.AutomaticPojoCodec.decode(AutomaticPojoCodec.java:37) ~[bson-3.7.1.jar:?]
      ... 46 more
  </code></pre>