This is a common problem – the error is in Illuminate/Container/Container.php (line 736 or 741).
Common reason: spaces in environment variable values in .env file
Two other fixes that have worked for me:
- after an apt-get upgrade on Homestead, installing the php7.0-mbstring package fixed it (Laravel needs four PHP extensions: OpenSSL, PDO, Mbstring and Tokenizer)
- on another installation, changing syntax from:
'production' === env('APP_ENV')
in a ternary operator in config/app.php was the solution.