object composition without + sign

[MovaTech Today]

While working with grafonnet library, I have found one operation that is confusing for me. 

It look like the following: 

{} {
  field: 42
} {
  field: 43
}

I don't understand why it works, and the final object contains 2 fields. I could not find any references in docs. Could you help me to understand it -- is it a composition, object override construct or something else? 

I expected it as the following (with plus signs): 

{} + {
  field: 42
} + {
  field: 43
}