eventMulticaster.addDocumentListener() returns weird values

I wrote a code to send the changes made by the user to another end via socket.

For some reason the variable `newFragment` which is returned by `documentChanged(...)` returns very weird values. Sometimes it returns IntellijIdeaRulezzz but I get that it is probably a test string or something but sometimes it returns this weird json file connected to this file schema-catalog.json or some other json files. All I need is to receive the changes, where these values come from???

    fun listenToChanges(filename: String) { // filename is file that currently its changes are listened to
        println("Listening to changes on $filename")

        val disposable = Disposer.newDisposable(ApplicationManager.getApplication(), "RequestedPagesState.myDocumentListenerDisposable")
        EditorFactory.getInstance().eventMulticaster.addDocumentListener(object : DocumentListener {
            override fun documentChanged(event: DocumentEvent) {
                super.documentChanged(event)
                val document = event.document
                val offset = event.offset
                if (!event.isWholeTextReplaced) { // Normal change
                    sendWriteSocketData(event.oldRange, event.newRange, event.newFragment, filename)
                } else { // Whole text is replaced
                    println("Whole text has replaced")
                }
            }

        }, disposable)
        myDocumentManagerListenerDisposable = disposable
    }