Use null instead of comparing with empty lists

src/ShellCheck/Analytics.hs

@@ -563,7 +563,7 @@ checkShebang params (T_Annotation _ list t) =
     isOverride _ = False
 checkShebang params (T_Script _ (T_Literal id sb) _) = execWriter $ do
     unless (shellTypeSpecified params) $ do
-        when (sb == "") $
+        when (null sb) $
             err id 2148 "Tips depend on target shell and yours is unknown. Add a shebang."
         when (executableFromShebang sb == "ash") $
             warn id 2187 "Ash scripts will be checked as Dash. Add '# shellcheck shell=dash' to silence."
@@ -2332,7 +2332,7 @@ checkWhileReadPitfalls _ (T_WhileExpression id [command] contents)
     checkMuncher _ = return ()
 
     stdinRedirect (T_FdRedirect _ fd _)
-        | fd == "" || fd == "0" = True
+        | null fd || fd == "0" = True
     stdinRedirect _ = False
 checkWhileReadPitfalls _ _ = return ()
 

src/ShellCheck/AnalyzerLib.hs

@@ -643,7 +643,7 @@ getModifiedVariableCommand base@(T_SimpleCommand id cmdPrefix (T_NormalWord _ (T
     getModifierParam _ _ = []
 
     letParamToLiteral token =
-          if var == ""
+          if null var
             then []
             else [(base, token, var, DataString $ SourceFrom [stripEqualsFrom token])]
         where var = takeWhile isVariableChar $ dropWhile (`elem` "+-") $ concat $ oversimplify token
@@ -952,7 +952,7 @@ getOpts string flags = process flags
         takesArg <- Map.lookup flag1 flagMap
         if takesArg
             then do
-                guard $ flag2 == ""
+                guard $ null flag2
                 more <- process rest
                 return $ (flag1, token2) : more
             else do

src/ShellCheck/Checker.hs

@@ -198,11 +198,11 @@ prop_optionDisablesBadShebang =
                 }
 
 prop_annotationDisablesBadShebang =
-    [] == check "#!/usr/bin/python\n# shellcheck shell=sh\ntrue\n"
+    null $ check "#!/usr/bin/python\n# shellcheck shell=sh\ntrue\n"
 
 
 prop_canParseDevNull =
-    [] == check "source /dev/null"
+    null $ check "source /dev/null"
 
 prop_failsWhenNotSourcing =
     [1091, 2154] == check "source lol; echo \"$bar\""
@@ -218,7 +218,7 @@ prop_worksWhenDotting =
 
 -- FIXME: This should really be giving [1093], "recursively sourced"
 prop_noInfiniteSourcing =
-    [] == checkWithIncludes  [("lib", "source lib")] "source lib"
+    null $ checkWithIncludes  [("lib", "source lib")] "source lib"
 
 prop_canSourceBadSyntax =
     [1094, 2086] == checkWithIncludes [("lib", "for f; do")] "source lib; echo $1"
@@ -239,10 +239,10 @@ prop_recursiveParsing =
     [1037] == checkRecursive [("lib", "echo \"$10\"")] "source lib"
 
 prop_nonRecursiveAnalysis =
-    [] == checkWithIncludes [("lib", "echo $1")] "source lib"
+    null $ checkWithIncludes [("lib", "echo $1")] "source lib"
 
 prop_nonRecursiveParsing =
-    [] == checkWithIncludes [("lib", "echo \"$10\"")] "source lib"
+    null $ checkWithIncludes [("lib", "echo \"$10\"")] "source lib"
 
 prop_sourceDirectiveDoesntFollowFile =
     null $ checkWithIncludes
@@ -328,7 +328,7 @@ prop_optionIncludes4 =
     [2154] == checkOptionIncludes (Just [2154]) "#!/bin/sh\n var='a b'\n echo $var\n echo $bar"
 
 
-prop_readsRcFile = result == []
+prop_readsRcFile = null result
   where
     result = checkWithRc "disable=2086" emptyCheckSpec {
         csScript = "#!/bin/sh\necho $1",

src/ShellCheck/Checks/Commands.hs

@@ -345,7 +345,7 @@ returnOrExit multi invalid = (f . arguments)
             invalid (getId value)
     f _ = return ()
 
-    isInvalid s = s == "" || any (not . isDigit) s || length s > 5
+    isInvalid s = null s || any (not . isDigit) s || length s > 5
         || let value = (read s :: Integer) in value > 255
 
     literal token = fromJust $ getLiteralStringExt lit token
@@ -706,7 +706,7 @@ checkReadExpansions = CommandCheck (Exactly "read") check
     options = getGnuOpts flagsForRead
     getVars cmd = fromMaybe [] $ do
         opts <- options cmd
-        return [y | (x,y) <- opts, x == "" || x == "a"]
+        return [y | (x,y) <- opts, null x || x == "a"]
 
     check cmd = mapM_ warning $ getVars cmd
     warning t = potentially $ do
@@ -1057,7 +1057,7 @@ checkSudoRedirect = CommandCheck (Basename "sudo") f
             Just (T_Redirecting _ redirs _) ->
                 mapM_ warnAbout redirs
     warnAbout (T_FdRedirect _ s (T_IoFile id op file))
-        | (s == "" || s == "&") && not (special file) =
+        | (null s || s == "&") && not (special file) =
         case op of
             T_Less _ ->
               info (getId op) 2024

src/ShellCheck/Parser.hs

@@ -3169,7 +3169,7 @@ readScriptFile sourced = do
             Nothing -> parseProblemAt pos ErrorC 1008 "This shebang was unrecognized. ShellCheck only supports sh/bash/dash/ksh. Add a 'shell' directive to specify."
 
     isValidShell s =
-        let good = s == "" || any (`isPrefixOf` s) goodShells
+        let good = null s || any (`isPrefixOf` s) goodShells
             bad = any (`isPrefixOf` s) badShells
         in
             if good