Deprecation notice in file_encrypt_field_config_presave()

Problem/Motivation

I'm noticing the following deprecation notice while installing from existing config:

Deprecated function: strpos(): Non-string needles will be interpreted as strings in the future. Use an explicit chr() call to preserve the current behavior in file_encrypt_field_config_presave() (line 67 of modules/contrib/file_encrypt/file_encrypt.module).
file_encrypt_field_config_presave(Object)
call_user_func_array('file_encrypt_field_config_presave', Array) (Line: 403)
Drupal\Core\Extension\ModuleHandler->invokeAll('field_config_presave', Array) (Line: 347)
Drupal\Core\Config\Entity\ConfigEntityStorage->invokeHook('presave', Object) (Line: 500)
Drupal\Core\Entity\EntityStorageBase->doPreSave(Object) (Line: 454)
Drupal\Core\Entity\EntityStorageBase->save(Object) (Line: 263)
Drupal\Core\Config\Entity\ConfigEntityStorage->save(Object) (Line: 395)
Drupal\Core\Entity\EntityBase->save() (Line: 616)
Drupal\Core\Config\Entity\ConfigEntityBase->save() (Line: 379)
Drupal\Core\Config\Entity\ConfigEntityStorage->importUpdate('field.field.node.myfield.te_files', Object, Object) (Line: 997)
Drupal\Core\Config\ConfigImporter->importInvokeOwner('', 'update', 'field.field.node.myfield.te_files') (Line: 783)
Drupal\Core\Config\ConfigImporter->processConfiguration('', 'update', 'field.field.node.myfield.te_files') (Line: 610)
Drupal\Core\Config\ConfigImporter->processConfigurations(Array) (Line: 514)
Drupal\Core\Config\ConfigImporter->doSyncStep('processConfigurations', Array) (Line: 490)
Drupal\Core\Config\ConfigImporter->import() (Line: 2445)
install_config_revert_install_changes(Array) (Line: 695)
install_run_task(Array, Array) (Line: 570)
install_run_tasks(Array, NULL) (Line: 118)
install_drupal(Object) (Line: 44)

Steps to reproduce

Install a D8 site from existing config where at least one file field is configured to use File Encrypt.
(I suspect upon debugging we'll identify better steps to reproduce this deprecation notice as the issue is better understood.)

Proposed resolution

Address deprecation notice.

Remaining tasks

• Debug
• Submit patch

User interface changes

None.

API changes

None.

Data model changes

None.