Interface Definition: Expression evaluation error : Invalid index type: Record field uuid: d6891dd4-40e4-47cc-8592-87a110d7d202 Record type uuid: ae7e0134-4b01-4908-b073-ff4a9d7b184d Relationship path: null

actually i am facing the error mentioned .. i dnt know why i cant directly pass the values 

  local!exisitngLinkData: if(isnull(local!existingData['recordType!PRO Viable Lead.fields.viableLeadId']),{},rule!PRO_qrtExclusiveVendors(
    viableLeadiD: local!existingData['recordType!PRO Viable Lead.fields.viableLeadId']
  ).data),
  
  local!lookupRefId: if(
    a!isNullOrEmpty(
      local!exisitngLinkData['recordType!PRO Lead Exclusive Vendor.fields.lookupRefId']
    ),
    {},
    local!exisitngLinkData['recordType!PRO Lead Exclusive Vendor.fields.lookupRefId']
  ),

i dnt know why i am getting this error ... can anybdy help me on this ... i know vlaue i am getting is null .. what should i do ..