Resolve notice on undefined index

fixes #384

phpstan.neon

@@ -2,5 +2,6 @@ parameters:
     level: max
     ignoreErrors:
         - '#Method phpDocumentor\\Reflection\\DocBlock\\StandardTagFactory::createTag\(\) should return phpDocumentor\\Reflection\\DocBlock\\Tag but returns mixed#'
+        - '#Offset 2 on array\{string, 28, int\} on left side of \?\? always exists and is not nullable\.#'
     paths:
         - src

src/DocBlock/Tags/Factory/AbstractPHPStanFactory.php

@@ -104,12 +104,12 @@ class AbstractPHPStanFactory implements Factory
                 $fixed[] = [
                     rtrim($token[Lexer::VALUE_OFFSET], " \t"),
                     Lexer::TOKEN_PHPDOC_EOL,
-                    $token[2],
+                    $token[2] ?? 0,
                 ];
                 $fixed[] = [
                     ltrim($token[Lexer::VALUE_OFFSET], "\n\r"),
                     Lexer::TOKEN_HORIZONTAL_WS,
-                    $token[2] + 1,
+                    ($token[2] ?? 0) + 1,
                 ];
                 continue;
             }