graphparser: only print filter arguments if they are non-NULL

libavfilter/graphparser.c

@@ -126,7 +126,10 @@ static int create_filter(AVFilterContext **filt_ctx, AVFilterGraph *ctx, int ind
     ret = avfilter_init_str(*filt_ctx, args);
     if (ret < 0) {
         av_log(log_ctx, AV_LOG_ERROR,
-               "Error initializing filter '%s' with args '%s'\n", filt_name, args);
+               "Error initializing filter '%s'", filt_name);
+        if (args)
+            av_log(log_ctx, AV_LOG_ERROR, " with args '%s'", args);
+        av_log(log_ctx, AV_LOG_ERROR, "\n");
         return ret;
     }