Fix: prompt of expert mode (#3168)

web/app/components/app/configuration/index.tsx

         const promptMode = modelConfig.prompt_type === PromptMode.advanced ? PromptMode.advanced : PromptMode.simple
         doSetPromptMode(promptMode)
         if (promptMode === PromptMode.advanced) {
-          setChatPromptConfig(modelConfig.chat_prompt_config || clone(DEFAULT_CHAT_PROMPT_CONFIG) as any)
+          if (modelConfig.chat_prompt_config && modelConfig.chat_prompt_config.prompt.length > 0)
+            setChatPromptConfig(modelConfig.chat_prompt_config)
+          else
+            setChatPromptConfig(clone(DEFAULT_CHAT_PROMPT_CONFIG) as any)
           setCompletionPromptConfig(modelConfig.completion_prompt_config || clone(DEFAULT_COMPLETION_PROMPT_CONFIG) as any)
           setCanReturnToSimpleMode(false)
         }

web/config/index.ts

 /* eslint-disable import/no-mutable-exports */
 import { InputVarType } from '@/app/components/workflow/types'
 import { AgentStrategy } from '@/types/app'
+import { PromptRole } from '@/models/debug'
 
 export let apiPrefix = ''
 export let publicApiPrefix = ''
 ]
 
 export const DEFAULT_CHAT_PROMPT_CONFIG = {
-  prompt: [],
+  prompt: [
+    {
+      role: PromptRole.system,
+      text: '',
+    },
+  ],
 }
 
 export const DEFAULT_COMPLETION_PROMPT_CONFIG = {