PHP 8.0 > String to Number Comparison.

When $previousIndent was equal to 0, and $matches['indent'] = "    "

PHP(before 8.0)> (0 != "    ") ==> false
PHP8.0+ > (0 != "     ")  ==> true

In order to keep "false" value we avoid "0" as a valid value.

More details here why here:
https://www.php.net/manual/en/migration80.incompatible.php

Author: Tybaze

lib/yaml/sfYamlParser.class.php

@@ -474,7 +474,7 @@ protected function parseFoldedScalar($separator, $indicator = '', $indentation =
 
       if (preg_match('#^(?P<indent> {'.strlen($textIndent).',})(?P<text>.+)$#u', $this->currentLine, $matches))
       {
-        if (' ' == $separator && $previousIndent != $matches['indent'])
+        if (' ' == $separator && ($previousIndent && $previousIndent != $matches['indent']))
         {
           $text = substr($text, 0, -1)."\n";
         }