Bug Report: NullPointerException when creating Db2Container

[k-higuchi0440]

Hi, I would like to report a bug below!

Description

The Db2Container class throws a NullPointerException during instantiation due to calling inherited username and password methods before the underlying container is initialized.

Reproduction Code

  import com.dimafeng.testcontainers.Db2Container
  import org.testcontainers.utility.DockerImageName

  // This will throw NullPointerException
  val container = Db2Container(
    dockerImageName = DockerImageName.parse("icr.io/db2_community/db2:11.5.9.0")
  )

Error Message

  java.lang.NullPointerException: Cannot invoke "org.testcontainers.containers.JdbcDatabaseContainer.getUsername()" because the return value of "com.dimafeng.testcontainers.SingleContainer.underlyingUnsafeContainer()" is null
    at com.dimafeng.testcontainers.JdbcDatabaseContainer.username(JdbcDatabaseContainer.scala:17)
    at com.dimafeng.testcontainers.Db2Container.(Db2Container.scala:19)

Root Cause

In the Db2Container.scala source code, lines 19-20 call username and password:

case class Db2Container(
  dockerImageName: DockerImageName = ...,
  dbName: String = ...,
  dbUsername: String = Db2Container.defaultUsername,    // constructor parameter
  dbPassword: String = Db2Container.defaultPassword,    // constructor parameter
  ...
) extends SingleContainer[JavaDb2Container] with JdbcDatabaseContainer {

  override val container: JavaDb2Container = {
    val c = new JavaDb2Container(dockerImageName)
    c.withDatabaseName(dbName)
    c.withUsername(username)  // ← JdbcDatabaseContainer method is called
    c.withPassword(password)  // ← same as above
    c.acceptLicense()
    ...
  }
}

These username and password are methods from the JdbcDatabaseContainer trait that call underlyingUnsafeContainer.getUsername() and underlyingUnsafeContainer.getPassword(). However, since these are called during container field initialization, underlyingUnsafeContainer is still null, causing a NullPointerException.

Fix Proposal

Change lines 19-20 to use the constructor parameters directly:

  c.withUsername(dbUsername)
  c.withPassword(dbPassword) 

Environment

• testcontainers-scala-db2: 0.43.6
• Scala: 2.13
• Error occurs in both TestContainersForAll and manual container creation

My environmennt is a little old but this bug exists in the current master branch and affects all versions using the current implementation. The issue prevents any usage of the Db2Container class.