Add CombinedConfig.getVal that raises an exception if the config key is not found.

cliutils.nim

@@ -10,7 +10,7 @@ type
 
   TermColor = ForegroundColor or BackgroundColor
 
-proc getVal*(cfg: CombinedConfig, key, default: string): string =
+proc getVal*(cfg: CombinedConfig, key: string): string =
   let argKey = "--" & key
   let envKey = key.replace('-', '_').toUpper
   let jsonKey = key.replace(re"(-\w)", proc (m: RegexMatch): string = ($m)[1..1].toUpper)
@@ -27,8 +27,11 @@ proc getVal*(cfg: CombinedConfig, key, default: string): string =
     of JNull: return ""
     of JObject: return $node
     of JArray: return $node
-  else: return default
+  else: raise newException(ValueError, "cannot find a configuration value for \"" & key & "\"")
 
+proc getVal*(cfg: CombinedConfig, key, default: string): string =
+  try: return getVal(cfg, key)
+  except: return default
 
 proc loadEnv*(): StringTableRef =
   result = newStringTable()