chore: improve get-create-field in justfile

Author: nyurik

justfile

@@ -125,7 +125,7 @@ fmt-toml *args:  (cargo-install 'cargo-sort')
 
 # Get any package's field from the metadata
 get-crate-field field package=main_crate:  (assert-cmd 'jq')
-    cargo metadata --format-version 1 | jq -e -r '.packages | map(select(.name == "{{package}}")) | first | .{{field}} | select(. != null)'
+    cargo metadata --format-version 1 | jq -e -r '.packages | map(select(.name == "{{package}}")) | first | .{{field}} // error("Field \"{{field}}\" is missing in Cargo.toml for package {{package}}")'
 
 # Get the minimum supported Rust version (MSRV) for the crate
 get-msrv package=main_crate:  (get-crate-field 'rust_version' package)