Error - typeerror: cannot read property 'then' of null - node js

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Javascript

Node.js

I have below code snippet which is giving me an error. I am getting a response back from getFilteredList which is of lenght 1 and it has a proper json data. But not sure why its giving error.

TypeError: Cannot read property 'then' of null

getFilteredList(group, feature).then(r=>{ //here I am getting error. 
    if(r.data.response_code == "1")
    {
      const columnName = "ColumnName";
      const Codes = r.data.response_message.map(x => x[columnName]);
      Codes.forEach(code => {
        let store = getStoreValue(code);
        getDetailsById(id, datastore)
        .then(r=>{
          res.status(200).send(r.data);
        }).catch(e=>{
          parseError(e, res);
        });
      })
    }
  }).catch(e=>{
      parseError(e, res);
    });
}

What I have tried:

getFilteredList() a another node js service which is returning a data when I tested it using Saop UI. I can see it in logs as well of application. I am not getting why it is saying null though having a data
Below is sample data it returns.

{"CODE":"AGR","GRP":"LEND","FEAT_CODE":"SRC_AGREE","GROUP_NAME":"Prop","FEA_NAME":"Property","DISPLAY_NAME":"Property","ROLE_CODE":"LE"}