how PsiAugmentProvider return psiClass ? Follow

override fun <Psi : PsiElement> getAugments(
psiElement: PsiElement,
type: Class<Psi>,
nameHint: String?
): MutableList<Psi> {
    var emptyResult = ArrayList<Psi>();

    if (!PsiField::class.java.isAssignableFrom(type)) {
        return emptyResult;
    }

    if ((psiElement is PsiClass) == false) {
        return emptyResult;
    }
    var psiClass = psiElement as PsiClass;
 
    // create field. it's ok
    val psiField: PsiField = MyFieldUtils.createCacheField(psiClass, "hello")
    val psiElementList: MutableList<PsiElement> = ArrayList()
    psiElementList.add(psiField)

    var desginName = psiClass.name + "Desgin"
    // TODO How to add ?
    var javaFile: PsiFile = PsiFileFactory.getInstance(psiElement.project)
        .createFileFromText(
            "${desginName}.java", JavaFileType.INSTANCE, """
            package com.youtube.geekific
             class ${desginName}{
               public String name(){
                  return "";
               }
            }
        """.trimIndent()
        )
    return (psiElementList as MutableList<Psi>);
}