[BUG] Can't override data for sequential agents

[muditguptacode]

Describe the bug When using the API to override parameters in sequential agents or LLM nodes, the ability to specify multiple values for a config parameter by specifying the node ids does not seem to work correctly.

Example:

This overrideConfig works correctly:

 overrideConfig: {
      sessionId:  '<some session id>',
      systemMessagePrompt: 'you are cat, you can only response with meows',
      qdrantCollection: {
        qdrant_2: 'vectorCollectionName'
      }
    }

BUT this one causes an error: (Error: predictionsServices.buildChatflow - Error buildAgentGraph - message.content.map is not a function)

 overrideConfig: {
      sessionId: '<some session id>',
      systemMessagePrompt: {
          seqAgent_0: 'you are cat, you can only response with meows'
     },
      qdrantCollection: {
        qdrant_2: 'vectorCollectionName'
      }
}

To Reproduce Steps to reproduce the behavior:

1. Create a flow using sequential agents or LLM nodes
2. Try providing override config values by specifying node id

Expected behavior The flow should accept the override values and return the prediction result

[HenryHengZJ]

Do you have a example flow?

I tried testing and it works as expected:

1.) Has an agentflow with 2 agents:

2.) Test via Postman (override system prompt for agent_2):

3.) Verify on langsmith: