When we define parameters in a Logic apps by default they need a value to be passed by calling object. If you want to make a parameter to accept null value as well then define them as below.
default declaration:
{
"properties": {
"packageName": {
"type": "string"
}
"type": "object"
}
}
Allow null value:
{
"properties": {
"packageName": {
"type":["string", "null"]
}
"type": "object"
}
}