Object of class __PHP_Incomplete_Class could not be converted to string

[ilyahoilik]

The problem appeared this morning (probably after upgrading PHP to 7.2.0RC3 or after upgrading this plugin to the newly released version).

How to reproduce:
Open any PHP file and type return<space>. As a result, the Output panel appears with the following error:

Any idea how could I fix it?

[Error - 4:26:33 PM] Request textDocument/completion failed.
  Message: ErrorException: Object of class __PHP_Incomplete_Class could not be converted to string in /home/ilyahoilik/.vscode/extensions/felixfbecker.php-intellisense-1.5.3/vendor/felixfbecker/language-server/src/Protocol/CompletionItem.php:152
Stack trace:
#0 /home/ilyahoilik/.vscode/extensions/felixfbecker.php-intellisense-1.5.3/vendor/felixfbecker/language-server/src/Protocol/CompletionItem.php(152): {closure}(4096, 'Object of class...', '/home/ilyahoili...', 152, Array)
#1 /home/ilyahoilik/.vscode/extensions/felixfbecker.php-intellisense-1.5.3/vendor/felixfbecker/language-server/src/CompletionProvider.php(338): LanguageServer\Protocol\CompletionItem::fromDefinition(Object(LanguageServer\Definition))
#2 /home/ilyahoilik/.vscode/extensions/felixfbecker.php-intellisense-1.5.3/vendor/felixfbecker/language-server/src/Server/TextDocument.php(358): LanguageServer\CompletionProvider->provideCompletion(Object(LanguageServer\PhpDocument), Object(LanguageServer\Protocol\Position))
#3 [internal function]: LanguageServer\Server\TextDocument->LanguageServer\Server\{closure}()
#4 /home/ilyahoilik/.vscode/extensions/felixfbecker.php-intellisense-1.5.3/vendor/sabre/event/lib/coroutine.php(70): Generator->send(Object(LanguageServer\PhpDocument))
#5 /home/ilyahoilik/.vscode/extensions/felixfbecker.php-intellisense-1.5.3/vendor/sabre/event/lib/Promise.php(242): Sabre\Event\{closure}(Object(LanguageServer\PhpDocument))
#6 /home/ilyahoilik/.vscode/extensions/felixfbecker.php-intellisense-1.5.3/vendor/sabre/event/lib/Loop/Loop.php(261): Sabre\Event\Promise->Sabre\Event\{closure}()
#7 /home/ilyahoilik/.vscode/extensions/felixfbecker.php-intellisense-1.5.3/vendor/sabre/event/lib/Loop/Loop.php(215): Sabre\Event\Loop\Loop->runNextTicks()
#8 /home/ilyahoilik/.vscode/extensions/felixfbecker.php-intellisense-1.5.3/vendor/sabre/event/lib/Loop/Loop.php(194): Sabre\Event\Loop\Loop->tick(true)
#9 /home/ilyahoilik/.vscode/extensions/felixfbecker.php-intellisense-1.5.3/vendor/sabre/event/lib/Loop/functions.php(122): Sabre\Event\Loop\Loop->run()
#10 /home/ilyahoilik/.vscode/extensions/felixfbecker.php-intellisense-1.5.3/vendor/felixfbecker/language-server/bin/php-language-server.php(102): Sabre\Event\Loop\run()
#11 {main}
  Code: -32603