Fix COARDS writer crash with empty string comments

CHANGELOG

@@ -1,3 +1,7 @@
+v1.0.2.9 (2024-04-??)
+=====================
+* (Bug) Fix crash in the COARDS writer when the comments are just an empty string
+
 v1.0.2.8 (2024-03-22)
 =====================
 * netCDF4 is now requried as part of the selftest option when installing

cchdo/hydro/legacy/coards/__init__.py

@@ -206,6 +206,8 @@ def get_coards_global_attributes(ds: xr.Dataset, *, profile_type: Literal["B", "
     )
 
     _comments = ds.attrs.get("comments", "").splitlines()
+    if len(_comments) == 0:
+        _comments = [""]
     og_header = "\n".join([_comments[0], *[f"#{line}" for line in _comments[1:]], ""])
     attrs["ORIGINAL_HEADER"] = og_header
 

cchdo/hydro/tests/test_accessors.py

@@ -25,6 +25,20 @@ def test_gen_fname_machinery(
     )
 
 
+def test_coards_no_comments():
+    # note that the differet bottle and sampno are intentional
+    test_data = b"""BOTTLE,test
+# some comment
+EXPOCODE,STNNBR,CASTNO,SAMPNO,BTLNBR,DATE,TIME,LATITUDE,LONGITUDE,CTDPRS
+,,,,,,,,,DBAR
+TEST          ,1       ,  1,1          ,2          ,20200101,0000,        0,        0,        0
+END_DATA
+"""
+    ds = read_exchange(test_data)
+    ds.attrs["comments"] = ""
+    ds.cchdo.to_coards()
+
+
 def test_exchange_bottle_round_trip():
     # note that the differet bottle and sampno are intentional
     test_data = b"""BOTTLE,test