fix(healthcheck): handle empty reports

runtime/autoload/health.vim

@@ -21,10 +21,17 @@ function! health#check(plugin_names) abort
           throw 'healthcheck_not_found'
         endif
         eval type == 'v' ? call(func, []) : luaeval(func)
+        " in the event the healthcheck doesn't return anything
+        " (the plugin author should avoid this possibility)
+        if len(s:output) == 0
+          throw 'healthcheck_no_return_value'
+        endif
       catch
         let s:output = []  " Clear the output
         if v:exception =~# 'healthcheck_not_found'
           call health#report_error('No healthcheck found for "'.name.'" plugin.')
+        elseif v:exception =~# 'healthcheck_no_return_value'
+          call health#report_error('The healthcheck report for "'.name.'" plugin is empty.')
         else
           call health#report_error(printf(
                 \ "Failed to run healthcheck for \"%s\" plugin. Exception:\n%s\n%s",

test/functional/fixtures/lua/test_plug/submodule_empty/health.lua

@@ -0,0 +1,7 @@
+local M = {}
+
+M.check = function()
+  return {}
+end
+
+return M

test/functional/plugin/health_spec.lua

@@ -153,6 +153,10 @@ describe('health.vim', function()
         ## report 2
           - OK: nothing to see here
 
+        test_plug.submodule_empty: require("test_plug.submodule_empty.health").check()
+        ========================================================================
+          - ERROR: The healthcheck report for "test_plug.submodule_empty" plugin is empty.
+
         test_plug.submodule_failed: require("test_plug.submodule_failed.health").check()
         ========================================================================
           - ERROR: Failed to run healthcheck for "test_plug.submodule_failed" plugin. Exception:
@@ -172,6 +176,16 @@ describe('health.vim', function()
         ]])
     end)
 
+    it("... including empty reports", function()
+      command("checkhealth test_plug.submodule_empty")
+      helpers.expect([[
+
+      test_plug.submodule_empty: require("test_plug.submodule_empty.health").check()
+      ========================================================================
+        - ERROR: The healthcheck report for "test_plug.submodule_empty" plugin is empty.
+      ]])
+    end)
+
     it("gracefully handles broken lua healthcheck", function()
       command("checkhealth test_plug.submodule_failed")
       local buf_lines = helpers.curbuf('get_lines', 0, -1, true)