How to handle map of maps in terraform if key is not present

[bptambake]

//list of keys
keys=[key1,key2,key3,key4,key5,key6,key7]

//map of maps
"map-of-maps":
{
"key1":
{
"k1": "v1"
},
"key3":
{
"k3": "v3"
},
"key4":
{
"k4": "v4"
},
"key6":
{
"k6": "v6"
}

}

i want to Iterate for the keys on this map-of-maps, but few of the key present in keys dont have corresponding value in map-of-maps and it is throwing error.
I need to handle the exception, if the key is not present in map-of-maps, it should return empty.

example: key5 is present in the list and it is not present in map-of-maps, while iterating using for loop it is throwing error.

var.mapofmaps is map of map of string with 4 elements
The given key does not identify an element in this collection value