allow empty word separator in passphrases (#597)

Allow the passphrase word separator to be the empty string `''`. 

This change recently merged [in the clients
repository](bitwarden/clients@bb031f6).

crates/bitwarden-generators/src/passphrase.rs

@@ -10,8 +10,6 @@ use crate::util::capitalize_first_letter;
 pub enum PassphraseError {
     #[error("'num_words' must be between {} and {}", minimum, maximum)]
     InvalidNumWords { minimum: u8, maximum: u8 },
-    #[error("'word_separator' cannot be empty")]
-    EmptyWordSeparator,
 }
 
 /// Passphrase generator request options.
@@ -69,10 +67,6 @@ impl PassphraseGeneratorRequest {
             });
         }
 
-        if self.word_separator.chars().next().is_none() {
-            return Err(PassphraseError::EmptyWordSeparator);
-        };
-
         Ok(ValidPassphraseGeneratorOptions {
             num_words: self.num_words,
             word_separator: self.word_separator,