Polish JacksonJsonDecoder

spring-web-reactive/src/main/java/org/springframework/core/codec/support/JacksonJsonDecoder.java

@@ -68,19 +68,15 @@ public class JacksonJsonDecoder extends AbstractDecoder<Object> {
 		JavaType javaType = typeFactory.constructType(elementType.getType());
 		ObjectReader reader = this.mapper.readerFor(javaType);
 
-		Flux<DataBuffer> stream = Flux.from(inputStream);
+		return this.preProcessor.decode(inputStream, elementType, mimeType, hints)
-		if (this.preProcessor != null) {
+				.map(dataBuffer -> {
-			stream = this.preProcessor.decode(inputStream, elementType, mimeType, hints);
-		}
-
-		return stream.map(dataBuffer -> {
 					try {
 						Object value = reader.readValue(dataBuffer.asInputStream());
 						DataBufferUtils.release(dataBuffer);
 						return value;
 					}
 					catch (IOException e) {
-				throw new CodecException("Error while reading the data", e);
+						return Flux.error(new CodecException("Error while reading the data", e));
 					}
 		});
 	}