[Hacker Rank] Warmup: Time Conversion solved ✅. Triying to fix sonarlint detected issues.

Author: Gonzalo Diaz

src/lib/exercises/src/hackerrank/warmup/time_conversion.c

@@ -9,6 +9,10 @@
 #include <string.h>
 
 char *HACKERRANK_WARMUP_firstN(const char *s, unsigned long n) {
+  if (s == NULL) {
+    return NULL;
+  }
+
   unsigned long len = strlen(s);
   if (n > len) {
     return NULL;

src/tests/unit/lib/hackerrank/warmup/time_conversion.test.cpp

@@ -34,6 +34,8 @@ TEST_CASE("time_conversion JSON Test Cases",
 
 TEST_CASE("time_conversion helper functions edge cases",
           "[hackerrank] [helper] [warmup]") {
+  CHECK(HACKERRANK_WARMUP_firstN(nullptr, 0) == nullptr);
+
   CHECK(HACKERRANK_WARMUP_firstN("", 10) == nullptr);
   CHECK(HACKERRANK_WARMUP_lastN("", 10) == nullptr);