tree-wide: drop a few == NULL and != NULL comparison

Our CODING_STYLE suggests not comparing with NULL, but relying on C's
downgrade-to-bool feature for that. Fix up some code to match these
guidelines. (This is not comprehensive, the coccinelle output for this
is unfortunately kinda borked)

src/basic/clock-util.c

@@ -73,7 +73,7 @@ int clock_set_hwclock(const struct tm *tm) {
 int clock_is_localtime(const char* adjtime_path) {
         _cleanup_fclose_ FILE *f;
 
-        if (adjtime_path == NULL)
+        if (!adjtime_path)
                 adjtime_path = "/etc/adjtime";
 
         /*

src/basic/device-nodes.c

@@ -40,7 +40,7 @@ int whitelisted_char_for_devnode(char c, const char *white) {
 int encode_devnode_name(const char *str, char *str_enc, size_t len) {
         size_t i, j;
 
-        if (str == NULL || str_enc == NULL)
+        if (!str || !str_enc)
                 return -EINVAL;
 
         for (i = 0, j = 0; str[i] != '\0'; i++) {

src/basic/ether-addr-util.c

@@ -71,7 +71,7 @@ int ether_addr_from_string(const char *s, struct ether_addr *ret, size_t *offset
                         if (s[pos] == '\0')                     \
                                 break;                          \
                         hexoff = strchr(hex, s[pos]);           \
-                        if (hexoff == NULL)                     \
+                        if (!hexoff)                            \
                                 break;                          \
                         assert(hexoff >= hex);                  \
                         x = hexoff - hex;                       \
@@ -99,7 +99,7 @@ int ether_addr_from_string(const char *s, struct ether_addr *ret, size_t *offset
         sep = s[strspn(s, hex)];
         if (sep == '\n')
                 return -EINVAL;
-        if (strchr(":.-", sep) == NULL)
+        if (!strchr(":.-", sep))
                 return -EINVAL;
 
         if (sep == '.') {

src/basic/fileio.c

@@ -140,7 +140,7 @@ int write_string_file_ts(
 
                 return r;
         } else
-                assert(ts == NULL);
+                assert(!ts);
 
         if (flags & WRITE_STRING_FILE_CREATE) {
                 f = fopen(fn, "we");
@@ -1191,7 +1191,7 @@ int tempfn_xxxxxx(const char *p, const char *extra, char **ret) {
         if (!filename_is_valid(fn))
                 return -EINVAL;
 
-        if (extra == NULL)
+        if (!extra)
                 extra = "";
 
         t = new(char, strlen(p) + 2 + strlen(extra) + 6 + 1);

src/basic/journal-importer.c

@@ -96,7 +96,7 @@ static int get_line(JournalImporter *imp, char **line, size_t *size) {
         assert(imp->state == IMPORTER_STATE_LINE);
         assert(imp->offset <= imp->filled);
         assert(imp->filled <= imp->size);
-        assert(imp->buf == NULL || imp->size > 0);
+        assert(!imp->buf || imp->size > 0);
         assert(imp->fd >= 0);
 
         for (;;) {
@@ -159,8 +159,8 @@ static int fill_fixed_size(JournalImporter *imp, void **data, size_t size) {
         assert(size <= DATA_SIZE_MAX);
         assert(imp->offset <= imp->filled);
         assert(imp->filled <= imp->size);
-        assert(imp->buf != NULL || imp->size == 0);
-        assert(imp->buf == NULL || imp->size > 0);
+        assert(imp->buf || imp->size == 0);
+        assert(!imp->buf || imp->size > 0);
         assert(imp->fd >= 0);
         assert(data);
 

src/basic/path-util.c

@@ -538,7 +538,7 @@ bool paths_check_timestamp(const char* const* paths, usec_t *timestamp, bool upd
 
         assert(timestamp);
 
-        if (paths == NULL)
+        if (!paths)
                 return false;
 
         STRV_FOREACH(i, paths) {

src/basic/time-util.c

@@ -893,7 +893,7 @@ int parse_timestamp(const char *t, usec_t *usec) {
         if (last_space != NULL && timezone_is_valid(last_space + 1))
                 tz = last_space + 1;
 
-        if (tz == NULL || endswith_no_case(t, " UTC"))
+        if (!tz || endswith_no_case(t, " UTC"))
                 return parse_timestamp_impl(t, usec, false);
 
         shared = mmap(NULL, sizeof *shared, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0);