Implemented CustomerData.addAccount()

fints4javaLib/src/main/kotlin/net/dankito/fints/FinTsClient.kt

@@ -808,9 +808,7 @@ open class FinTsClient @JvmOverloads constructor(
                     accountInfo.accountType, accountInfo.currency, accountHolderName, accountInfo.productName,
                     accountInfo.accountLimit, accountInfo.allowedJobNames)
 
-                val accounts = customer.accounts.toMutableList()
-                accounts.add(newAccount)
-                customer.accounts = accounts
+                customer.addAccount(newAccount)
             }
 
             // TODO: may also make use of other info

fints4javaLib/src/main/kotlin/net/dankito/fints/model/CustomerData.kt

@@ -11,7 +11,7 @@ open class CustomerData(
     val userId: String = customerId,
     var name: String = "",
     var iban: String? = null,
-    var accounts: List<AccountData> = listOf(),
+    val accounts: List<AccountData> = mutableListOf(),
     var updVersion: Int = UPDVersion.VersionNotReceivedYet,
     var supportedTanProcedures: List<TanProcedure> = listOf(),
     var selectedTanProcedure: TanProcedure = TanProcedureNotSelected,
@@ -49,6 +49,11 @@ open class CustomerData(
     }
 
 
+    open fun addAccount(account: AccountData) {
+        (accounts as? MutableList)?.add(account)
+    }
+
+
     override fun toString(): String {
         return customerId
     }