Docker: If `DB_*` env var is unset, remove the corresponding setting

CHANGELOG.md

@@ -26,6 +26,8 @@
   * Support for unset variables without a default value is now deprecated.
     Please change all instances of `"${FOO}"` in your `settings.json` to
     `${FOO:null}` to keep the current behavior.
+  * The `DB_*` variable substitutions in `settings.json.docker` that previously
+    defaulted to `null` now default to "undefined".
 
 ### Notable enhancements
 

settings.json.docker

@@ -207,12 +207,12 @@
 
   "dbType": "${DB_TYPE:dirty}",
   "dbSettings": {
-    "host":     "${DB_HOST:null}",
-    "port":     "${DB_PORT:null}",
-    "database": "${DB_NAME:null}",
-    "user":     "${DB_USER:null}",
-    "password": "${DB_PASS:null}",
-    "charset":  "${DB_CHARSET:null}",
+    "host":     "${DB_HOST:undefined}",
+    "port":     "${DB_PORT:undefined}",
+    "database": "${DB_NAME:undefined}",
+    "user":     "${DB_USER:undefined}",
+    "password": "${DB_PASS:undefined}",
+    "charset":  "${DB_CHARSET:undefined}",
     "filename": "${DB_FILENAME:var/dirty.db}"
   },