Fix type error

src/Monolog/Handler/SocketHandler.php

@@ -265,6 +265,10 @@ class SocketHandler extends AbstractProcessingHandler
             throw new \LogicException('streamSetChunkSize called but $this->resource is not a resource');
         }
 
+        if (null === $this->chunkSize) {
+            throw new \LogicException('streamSetChunkSize called but $this->chunkSize is not set');
+        }
+
         return stream_set_chunk_size($this->resource, $this->chunkSize);
     }