diff --git a/R/resolve.R b/R/resolve.R
index 0fd85c2..5ebafca 100644
--- a/R/resolve.R
+++ b/R/resolve.R
@@ -475,13 +475,18 @@ query_sysreqs <- function(rang, os = "ubuntu-20.04") {
     }
     pkgs <- .memo_search_bioc(bioc_version = "release")
     raw_sys_reqs <- pkgs$SystemRequirements[pkgs$Package %in% handles]
-    baseurl <- "https://sysreqs.r-hub.io/map/"
     singleline_sysreqs <- paste0(raw_sys_reqs[!is.na(raw_sys_reqs)], collapse = ", ")
     singleline_sysreqs <- gsub("\\n", " ", singleline_sysreqs)
+    .query_singleline_sysreqs(singleline_sysreqs = singleline_sysreqs, arch = arch)
+}
+
+.query_singleline_sysreqs <- function(singleline_sysreqs, arch = "DEB") {
+    baseurl <- "https://sysreqs.r-hub.io/map/"
     url <- utils::URLencode(paste0(baseurl, singleline_sysreqs))
-    checkable_cmds <- vapply(jsonlite::read_json(url), .extract_sys_package, character(1), arch = arch)
+    query_res <- jsonlite::read_json(url)
+    checkable_cmds <- vapply(query_res, .extract_sys_package, character(1), arch = arch)
     uncheckable_cmds <- .extract_uncheckable_sysreqs(singleline_sysreqs, arch = arch)
-    return(c(checkable_cmds, uncheckable_cmds))
+    c(checkable_cmds[!is.na(checkable_cmds)], uncheckable_cmds)
 }
 
 ## Not everything can be check from sysreqs DB, especially Bioc packages
@@ -506,6 +511,9 @@ query_sysreqs <- function(rang, os = "ubuntu-20.04") {
     } else {
         sys_pkg <- output[["buildtime"]]
     }
+    if (is.null(sys_pkg)) {
+        return(NA_character_)
+    }
     if (arch == "DEB") {
         return(paste0("apt-get install -y ", sys_pkg))
     }
diff --git a/tests/testdata/sysreqs_gmp.RDS b/tests/testdata/sysreqs_gmp.RDS
new file mode 100644
index 0000000..ffc98ab
Binary files /dev/null and b/tests/testdata/sysreqs_gmp.RDS differ
diff --git a/tests/testthat/test_resolve.R b/tests/testthat/test_resolve.R
index ddb6918..c34950b 100644
--- a/tests/testthat/test_resolve.R
+++ b/tests/testthat/test_resolve.R
@@ -225,10 +225,20 @@ test_that(".query_sysreqs_bioc with uncheckable info", {
     expect_true("apt-get install -y libbz2-dev" %in% x) ## uncheckable
     expect_true("apt-get install -y liblzma-dev" %in% x)
     expect_true("apt-get install -y make" %in% x) ## checkable
+    expect_false("apt-get install -y" %in% x) ## the null response from C++
     x <- .query_sysreqs_bioc("Rhtslib", "centos-7")
     expect_true("yum install -y libbz2-devel" %in% x)
     expect_true("yum install -y xz-devel" %in% x)
     expect_true("yum install -y make" %in% x)
+    expect_false("yum install -y" %in% x) ## the null response from C++
+    x <- .query_singleline_sysreqs("libxml2", "DEB")
+    expect_equal(x, "apt-get install -y libxml2-dev")
+    x <- .query_singleline_sysreqs("C++", "DEB")
+    expect_equal(x, character(0))
+    x <- readRDS("../testdata/sysreqs_gmp.RDS")
+    ## buildtime / runtime requirements
+    expect_equal(.extract_sys_package(x[[1]], arch = "DEB"),
+                 "apt-get install -y libgmp-dev")
 })
 
 test_that("issue 89", {