Meet error with logstash-logback-encoder7.1 But Not reproduce in other version

[Amanocino]

When I integrate logstash-logback-encoder7.1 in my springboot 2.6.6 ,meet such NullPointerException error in idea when running

Logging system failed to initialize using configuration from 'null'
java.lang.IllegalStateException: Logback configuration error detected: 
ERROR in ch.qos.logback.core.joran.action.NestedComplexPropertyIA - Could not create component [encoder] of type [net.logstash.logback.encoder.LogstashEncoder] java.lang.NullPointerException
ERROR in net.logstash.logback.appender.LogstashTcpSocketAppender[LOGSTASH] - No encoder was configured. Use <encoder> to specify the fully qualified class name of the encoder to use
	at org.springframework.boot.logging.logback.LogbackLoggingSystem.loadConfiguration(LogbackLoggingSystem.java:179)
	at org.springframework.boot.logging.AbstractLoggingSystem.initializeWithConventions(AbstractLoggingSystem.java:80)
	at org.springframework.boot.logging.AbstractLoggingSystem.initialize(AbstractLoggingSystem.java:60)
	at org.springframework.boot.logging.logback.LogbackLoggingSystem.initialize(LogbackLoggingSystem.java:132)
	at org.springframework.boot.context.logging.LoggingApplicationListener.initializeSystem(LoggingApplicationListener.java:313)
	at org.springframework.boot.context.logging.LoggingApplicationListener.initialize(LoggingApplicationListener.java:282)
	at org.springframework.boot.context.logging.LoggingApplicationListener.onApplicationEnvironmentPreparedEvent(LoggingApplicationListener.java:240)
	at org.springframework.boot.context.logging.LoggingApplicationListener.onApplicationEvent(LoggingApplicationListener.java:216)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:176)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:169)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:143)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:131)
	at org.springframework.boot.context.event.EventPublishingRunListener.environmentPrepared(EventPublishingRunListener.java:85)
	at org.springframework.boot.SpringApplicationRunListeners.lambda$environmentPrepared$2(SpringApplicationRunListeners.java:66)
	at java.util.ArrayList.forEach(ArrayList.java:1259)
	at org.springframework.boot.SpringApplicationRunListeners.doWithListeners(SpringApplicationRunListeners.java:120)
	at org.springframework.boot.SpringApplicationRunListeners.doWithListeners(SpringApplicationRunListeners.java:114)
	at org.springframework.boot.SpringApplicationRunListeners.environmentPrepared(SpringApplicationRunListeners.java:65)
	at org.springframework.boot.SpringApplication.prepareEnvironment(SpringApplication.java:339)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:297)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1312)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1301)
	at com.Application.main(Application.java:44)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at com.intellij.rt.execution.CommandLineWrapper.main(CommandLineWrapper.java:64)

my pom config is :

<parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.6</version>
        <relativePath/>
    </parent>

<dependency>
            <groupId>net.logstash.logback</groupId>
            <artifactId>logstash-logback-encoder</artifactId>
            <version>7.1</version>
        </dependency>

        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.2.9</version>
            <!-- Use runtime scope if the project does not have any compile-time usage of logback,
                 such as implementations of Appender, Encoder, Layout, TurboFilter, etc
            <scope>runtime</scope>
            -->
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-core</artifactId>
            <version>1.2.9</version>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-access</artifactId>
            <version>1.2.9</version>
        </dependency>

logback-spring.xml config is:

<appender name="LOGSTASH" class="net.logstash.logback.appender.LogstashTcpSocketAppender">
		<encoder class="net.logstash.logback.encoder.LogstashEncoder" >
		</encoder>
	</appender>

When i change the version of logstash-logback-encoder to 7.1.1 or 5.2, all will right, So I want to know why