Show Elm.Kernel as location when `report.path` is `null` in a general problem

ale_linters/elm/make.vim

@@ -22,6 +22,10 @@ function! ale_linters#elm#make#Handle(buffer, lines) abort
                 " General problem
                 let l:details = ale_linters#elm#make#ParseMessage(l:report.message)
 
+                if empty(l:report.path)
+                    let l:report.path = 'Elm.Kernel'
+                endif
+
                 if ale_linters#elm#make#FileIsBuffer(l:report.path)
                     call add(l:output, {
                                 \    'lnum': 1,
@@ -36,7 +40,6 @@ function! ale_linters#elm#make#Handle(buffer, lines) abort
                                 \    'detail': l:report.path ." ----------\n\n". l:details,
                                 \})
                 endif
-
             else
                 " Compilation errors
                 for l:error in l:report.errors

test/handler/test_elmmake_handler.vader

@@ -95,6 +95,12 @@ Execute(The elm make handler should handle errors in imported modules):
   \   {
   \     'lnum': 1,
   \     'type': 'E',
+  \     'text': "Elm.Kernel - error details\n\nstyled details",
+  \     'detail': "Elm.Kernel ----------\n\nerror details\n\nstyled details"
+  \   },
+  \   {
+  \     'lnum': 1,
+  \     'type': 'E',
   \     'text': "src/Module.elm:404 - error details\n\nstyled details",
   \     'detail': "src/Module.elm:404 ----------\n\nerror details\n\nstyled details"
   \   },
@@ -107,6 +113,12 @@ Execute(The elm make handler should handle errors in imported modules):
   \      "message": ["error details\n\n", { "string": "styled details" }]
   \    }',
   \   '{
+  \      "type": "error",
+  \      "path": null,
+  \      "title": "UNKNOWN IMPORT",
+  \      "message": ["error details\n\n", { "string": "styled details" }]
+  \    }',
+  \   '{
   \      "type": "compile-errors",
   \      "errors": [
   \        {