Fix nil body handling in fmt_error

Author: mfussenegger

lua/dap/utils.lua

@@ -4,7 +4,7 @@ local M = {}
 ---@param err ErrorResponse
 ---@return string?
 function M.fmt_error(err)
-  local body = err.body
+  local body = err.body or {}
   if body.error and body.error.showUser then
     local msg = body.error.format
     for key, val in pairs(body.error.variables or {}) do

tests/utils_spec.lua

@@ -1,3 +1,5 @@
+local utils = require('dap.utils')
+
 describe('utils.index_of', function()
   it('returns index of first item where predicate matches', function()
     local result = require('dap.utils').index_of(
@@ -79,4 +81,11 @@ describe('utils.fmt_error', function ()
       }
     }))
   end)
+
+  it('can handle response without body part', function()
+    local result = utils.fmt_error({
+      message = 'Bad things happen',
+    })
+    assert.are.same('Bad things happen', result)
+  end)
 end)