[BUG] AI Service fails when user message contains template variables

[langchain4j]

Describe the bug
AI Service fails when user message contains template variables.

Log and Stack trace

dev.langchain4j.exception.IllegalConfigurationException: Error: cannot find the value of the prompt template variable "{{it}}".
    at dev.langchain4j.exception.IllegalConfigurationException.illegalConfiguration(IllegalConfigurationException.java:12)
    at dev.langchain4j.service.DefaultAiServices.getValueOfVariableIt(DefaultAiServices.java:247)
    at dev.langchain4j.service.DefaultAiServices.findTemplateVariables(DefaultAiServices.java:223)
    at dev.langchain4j.service.DefaultAiServices.prepareUserMessage(DefaultAiServices.java:258)

To Reproduce

@AiService
public interface AiAssistant {

    TokenStream chat(@MemoryId String chatId, @UserMessage String userMessage);
}

assistant.chat("12345", "Text containing {{it}}");

Please complete the following information:

• LangChain4j version: latest

[KaisNeffati]

Hey ! Could you please clarify the expected behavior for this issue ?

[langchain4j]

Hi @KaisNeffati, it should not fail. In this case {{it}} (or any other variable) should not be treated as variable, but as a text

[anunnakian]

Hello @KaisNeffati, are you going to work on this issue ?

[KaisNeffati]

@anunnakian I was planning to do that, but I didn't have the time. Feel free to go for it if you'd like to

[anunnakian]

Ok thanks! @langchain4j could you assign me to this issue, I'll work on it today