following code:
```
.update(
bin_map__remove={123, 456}
)
```
Would fail if map is defined with non-nullable value type:
```
columns.Map(columns.BigInt, columns.Bytes, required=False, default={})
```

• Commit 0bfa545
• #1241: cqlengine: fix map remove feature for non-nullable values
• Branch master

dkropachev