fix: allow empty string subject keys in flag evaluation

Removed the validation that rejected empty subject keys, allowing legitimate
use cases where empty strings are valid subject identifiers. This fixes
assignment evaluation for users with empty string subject keys.

Author: leoromanovsky

Makefile

@@ -14,7 +14,7 @@ help: Makefile
 
 ## test-data
 testDataDir := eppoclient/test-data/
-branchName := main
+branchName := lr/false
 githubRepoLink := https://github.com/Eppo-exp/sdk-test-data.git
 .PHONY: test-data
 test-data:

eppoclient/client.go

@@ -359,10 +359,6 @@ func (ec *EppoClient) getBanditAction(
 }
 
 func (ec *EppoClient) getAssignment(ctx context.Context, config configuration, flagKey string, subjectKey string, subjectAttributes Attributes, variationType variationType) (interface{}, error) {
-	if subjectKey == "" {
-		return nil, fmt.Errorf("no subject key provided")
-	}
-
 	if flagKey == "" {
 		return nil, fmt.Errorf("no flag key provided")
 	}