Fix error raised by PHPStan

Author: Jean85

src/ErrorTypesParser.php

@@ -55,6 +55,10 @@ private function convertErrorConstants(string $expression): string
             return $errorConstant[0];
         }, $expression);
 
+        if (null === $output) {
+            throw new \InvalidArgumentException('Unable to parse error types string: ' . $expression);
+        }
+
         return $output;
     }
 

test/ErrorTypesParserTest.php

@@ -20,4 +20,12 @@ public function test_error_types_parser_throws_exception_for_unwanted_values()
         $this->expectException(\InvalidArgumentException::class);
         $ex->parse();
     }
+
+    public function test_error_types_parser_throws_exception_for_unparsable_values()
+    {
+        $ex = new ErrorTypesParser('something-wrong');
+
+        $this->expectException(\InvalidArgumentException::class);
+        $ex->parse();
+    }
 }