Map step lambda function with empty event is running a keyerror - amazon-web-services

Question

I'm writing a step function where lambda A queries a database and creates an array with s3bucket/s3key dictionaries for each one that needs to be processed.
For the processing I have a Map state that takes this s3bucket/s3key and do some processing.
For some reason, the event is coming empty resulting in an error in the Map state execution:
Here is the step function definition
{
"Comment": "A Hello World example of the Amazon States Language using Pass states",
"StartAt": "QueryTable",
"States": {
"QueryTable",": {
"Type": "Task",
"Resource": "arn:aws:states:::lambda:invoke",
"Parameters": {
"FunctionName": "arn:aws:lambda:...function:query_table:$LATEST"
},
"OutputPath": "$.Payload",
"Next": "ProcessDocuments"
},
"ProcessDocuments": {
"Type": "Map",
"ItemsPath": "$.toprocess",
"MaxConcurrency": 5,
"Iterator": {
"StartAt": "Process",
"States": {
"Process": {
"Type": "Task",
"Resource": "arn:aws:states:::lambda:invoke",
"Parameters": {
"FunctionName": "arn:aws:lambda:...:...:function:process:$LATEST"
},
"End": true
}
}
},
"End": true
}
}
}
And the error
{
"resourceType": "lambda",
"resource": "invoke",
"error": "KeyError",
"cause": {
"errorMessage": "'s3bucket'",
"errorType": "KeyError",
"stackTrace": [
" File \"/var/task/process.py\", line 260, in lambda_handler\n raise e\n",
" File \"/var/task/process.py\", line 230, in lambda_handler\n s3bucket, s3key = extract_event_data(event)\n",
" File \"/var/task/process.py\", line 125, in extract_event_data\n bucket = record['s3bucket']\n"
]
}
}
I read the ItemsPath and InputPath documentation. Also, used this example to see if I was using it incorrectly but it was no use.