Nextcloud not uploading documents from Android phone

### ⚠️ Before posting ⚠️

- [x] This is a **bug**, not a question or an enhancement.
- [x] I've [searched for similar issues](https://github.com/nextcloud/android/issues) and didn't find a duplicate.
- [x] I've written a clear and descriptive title for this issue, not just "Bug" or "Crash".
- [x] I agree to follow Nextcloud's [Code of Conduct](https://nextcloud.com/contribute/code-of-conduct/).

### Steps to reproduce

When I try to upload any document from my phone to my nextcloud account (when using the nextcloud app) it does nothing. When I tried to upload directly from a third app (example, sending an invoice from my banking app or WhatsApp to my Nextcloud), I receive an error message:

### Cause of error
```java
Exception in thread "main" java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.Set com.owncloud.android.ui.adapter.ReceiveExternalFilesAdapter.getFileNames()' on a null object reference
at com.owncloud.android.ui.activity.ReceiveExternalFilesActivity.lambda$getFileNameTextWatcher$6(ReceiveExternalFilesActivity.java:907)
at com.owncloud.android.ui.activity.ReceiveExternalFilesActivity.$r8$lambda$7aQSDlHWZ2ECuUzMqE_fcn8_TAk(Unknown Source:0)
at com.owncloud.android.ui.activity.ReceiveExternalFilesActivity$$ExternalSyntheticLambda11.invoke(D8$$SyntheticClass:0)
at com.nextcloud.utils.fileNameValidator.FileNameTextWatcher.afterTextChanged(FileNameTextWatcher.kt:43)
at android.widget.TextView.sendAfterTextChanged(TextView.java:12765)
at android.widget.TextView$ChangeWatcher.afterTextChanged(TextView.java:16366)
at android.text.SpannableStringBuilder.sendAfterTextChanged(SpannableStringBuilder.java:1278)
at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:578)
at androidx.emoji2.text.SpannableBuilder.replace(SpannableBuilder.java:308)
at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:508)
at androidx.emoji2.text.SpannableBuilder.replace(SpannableBuilder.java:298)
at androidx.emoji2.text.SpannableBuilder.replace(SpannableBuilder.java:48)
at android.view.inputmethod.BaseInputConnection.replaceTextInternal(BaseInputConnection.java:1026)
at android.view.inputmethod.BaseInputConnection.replaceText(BaseInputConnection.java:962)
at android.view.inputmethod.BaseInputConnection.commitText(BaseInputConnection.java:241)
at com.android.internal.inputmethod.EditableInputConnection.commitText(EditableInputConnection.java:220)
at android.view.inputmethod.InputConnectionWrapper.commitText(InputConnectionWrapper.java:207)
at android.view.inputmethod.RemoteInputConnectionImpl.lambda$commitText$17(RemoteInputConnectionImpl.java:670)
at android.view.inputmethod.RemoteInputConnectionImpl.$r8$lambda$jNtA8MXobPnaECkNr8D9WTYrxk0(Unknown Source:0)
at android.view.inputmethod.RemoteInputConnectionImpl$$ExternalSyntheticLambda46.run(D8$$SyntheticClass:0)
at android.os.Handler.handleCallback(Handler.java:959)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loopOnce(Looper.java:311)
at android.os.Looper.loop(Looper.java:408)
at android.app.ActivityThread.main(ActivityThread.java:9119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:627)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:970)

```

### App information
* ID: `com.nextcloud.client`
* Version: `330010090`
* Build flavor: `gplay`

### Device information
* Brand: `Infinix`
* Device: `Infinix-X6852`
* Model: `Infinix X6852`
* Id: `AP3A.240905.015.A2`
* Product: `X6852-OP`

### Firmware
* SDK: `35`
* Release: `15`
* Incremental: `170028`

### Expected behaviour

Upload the files correctly to my Nextcloud account.

### Actual behaviour

When I try to upload any document from my phone to my nextcloud account, it does nothing. When I tried to upload directly from a third app, I receive an error message:

### Cause of error
```java
Exception in thread "main" java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.Set com.owncloud.android.ui.adapter.ReceiveExternalFilesAdapter.getFileNames()' on a null object reference
at com.owncloud.android.ui.activity.ReceiveExternalFilesActivity.lambda$getFileNameTextWatcher$6(ReceiveExternalFilesActivity.java:907)
at com.owncloud.android.ui.activity.ReceiveExternalFilesActivity.$r8$lambda$7aQSDlHWZ2ECuUzMqE_fcn8_TAk(Unknown Source:0)
at com.owncloud.android.ui.activity.ReceiveExternalFilesActivity$$ExternalSyntheticLambda11.invoke(D8$$SyntheticClass:0)
at com.nextcloud.utils.fileNameValidator.FileNameTextWatcher.afterTextChanged(FileNameTextWatcher.kt:43)
at android.widget.TextView.sendAfterTextChanged(TextView.java:12765)
at android.widget.TextView$ChangeWatcher.afterTextChanged(TextView.java:16366)
at android.text.SpannableStringBuilder.sendAfterTextChanged(SpannableStringBuilder.java:1278)
at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:578)
at androidx.emoji2.text.SpannableBuilder.replace(SpannableBuilder.java:308)
at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:508)
at androidx.emoji2.text.SpannableBuilder.replace(SpannableBuilder.java:298)
at androidx.emoji2.text.SpannableBuilder.replace(SpannableBuilder.java:48)
at android.view.inputmethod.BaseInputConnection.replaceTextInternal(BaseInputConnection.java:1026)
at android.view.inputmethod.BaseInputConnection.replaceText(BaseInputConnection.java:962)
at android.view.inputmethod.BaseInputConnection.commitText(BaseInputConnection.java:241)
at com.android.internal.inputmethod.EditableInputConnection.commitText(EditableInputConnection.java:220)
at android.view.inputmethod.InputConnectionWrapper.commitText(InputConnectionWrapper.java:207)
at android.view.inputmethod.RemoteInputConnectionImpl.lambda$commitText$17(RemoteInputConnectionImpl.java:670)
at android.view.inputmethod.RemoteInputConnectionImpl.$r8$lambda$jNtA8MXobPnaECkNr8D9WTYrxk0(Unknown Source:0)
at android.view.inputmethod.RemoteInputConnectionImpl$$ExternalSyntheticLambda46.run(D8$$SyntheticClass:0)
at android.os.Handler.handleCallback(Handler.java:959)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loopOnce(Looper.java:311)
at android.os.Looper.loop(Looper.java:408)
at android.app.ActivityThread.main(ActivityThread.java:9119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:627)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:970)

```

### App information
* ID: `com.nextcloud.client`
* Version: `330010090`
* Build flavor: `gplay`

### Device information
* Brand: `Infinix`
* Device: `Infinix-X6852`
* Model: `Infinix X6852`
* Id: `AP3A.240905.015.A2`
* Product: `X6852-OP`

### Firmware
* SDK: `35`
* Release: `15`
* Incremental: `170028`

### Android version

15.1.2

### Device brand and model

Infinix 40 note

### Stock or custom OS?

Stock

### Nextcloud android app version

33.1.0

### Nextcloud server version

33.0.2

### Using a reverse proxy?

I don't know

### Android logs

_No response_

### Server error logs

```bash

```

### Additional information

_No response_