Javassist byte code instrumentation creates NoClassDefFoundError during runtime for a Springboot configuration class

Question

I was trying to modify a SpringBoot configuration java class during build time using javassist with gradle build. My intention is to remove a dependency jar(spring security) for a SpringBoot application based on a build configuration. For that first I had removed the method which uses the spring security Authentication class from the configuration class during build time with javassist using the following code.

ClassPool pool = ClassPool.getDefault();
CtClass cc = pool.get("com.xxx.xxx.SpringDataConfig");
cc.removeMethod(cc.getDeclaredMethod("auditor"));
cc.writeFile("./build/classes/java/main");

and the gradle task as

task applyCodeChange(type: JavaExec) {
    group = "Execution"
    description = "Code config"
    classpath = sourceSets.main.runtimeClasspath
    main = "com.xxx.xxx.CodeConfig"
  }
it.tasks.jar.dependsOn it.tasks.applyCodeChange

after executing the build task for that particular project. The resultant jar will have the modified class file without that method(verified by using Java decompiler). But when I tried to run that jar, I am facing the NoClassDefFoundError for the dependency which was used by that method. Also I could see the Import statement inside the decompiled class file for that dependency.

Below is the method which I was trying to remove.

 public AuditorAware<String> auditor() {
    Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
    return () -> Optional.ofNullable(authentication.getName());
  }

I could see always

import org.springframework.security.core.Authentication

in the decompiled class, but not the org.springframework.security.core.context.SecurityContextHolder. I had also confirmed no other methods in that class uses Authentication class in that file and always the java.lang.NoClassDefFoundError is for org/springframework/security/core/Authentication during the runtime of that application.