Added regression test

Author: staabm

tests/PHPStan/Analyser/nsrt/bug-11854.php

@@ -0,0 +1,18 @@
+<?php declare(strict_types = 1);
+
+namespace Bug11854;
+
+use function PHPStan\Testing\assertType;
+
+class HelloWorld
+{
+	public function sayHello(): void
+	{
+		$arr = [];
+		$arr[] = rand(0,1) ? 'A' : 'B';
+		$arr[] = rand(0,1) ? 'C' : '';
+
+		assertType("array{'A'|'B', ''|'C'}", $arr);
+		assertType("'A '|'A C'|'B '|'B C'", implode(' ', $arr));
+	}
+}