Make fixing ignore empty output better

autoload/ale/fix.vim

@@ -114,9 +114,11 @@ function! s:HandleExit(job_id, exit_code) abort
     " otherwise skip this job and use the input from before.
     "
     " We'll use the input from before for chained commands.
-    let l:input = l:chain_callback is v:null && !empty(l:job_info.output)
-    \   ? l:job_info.output
-    \   : l:job_info.input
+    if l:chain_callback is v:null && !empty(split(join(l:job_info.output)))
+        let l:input = l:job_info.output
+    else
+        let l:input = l:job_info.input
+    endif
 
     let l:next_index = l:chain_callback is v:null
     \   ? l:job_info.callback_index + 1

test/test_ale_fix.vader

@@ -105,6 +105,11 @@ Before:
     return {'command': ''}
   endfunction
 
+  " echo will output a single blank line, and we should ingore it.
+  function! IgnoredEmptyOutput(buffer, output)
+    return {'command': 'echo'}
+  endfunction
+
   function! SetUpLinters()
     call ale#linter#Define('testft', {
     \ 'name': 'testlinter',
@@ -149,6 +154,7 @@ After:
   delfunction ChainEndSkipped
   delfunction SetUpLinters
   delfunction GetLastMessage
+  delfunction IgnoredEmptyOutput
 
   call ale#test#RestoreDirectory()
 
@@ -568,3 +574,12 @@ Expect(The lines should be the same):
   a
   b
   c
+
+Execute(Empty output should be ignored):
+  let g:ale_fixers.testft = ['IgnoredEmptyOutput']
+  ALEFix
+
+Expect(The lines should be the same):
+  a
+  b
+  c