Add proper error message for null result when value expected

Without this check, the code would proceed to call Normalize() on a null result, causing an unclear failure that doesn't explain the actual problem.

Author: stringintech

runner/runner.go

@@ -233,6 +233,10 @@ func validateResponseForSuccess(test TestCase, resp *Response) error {
 		return nil
 	}
 
+	if resp.Result.IsNullOrOmitted() {
+		return fmt.Errorf("expected result with value, got null or omitted result")
+	}
+
 	expectedNorm, err := test.ExpectedResponse.Result.Normalize()
 	if err != nil {
 		return fmt.Errorf("failed to normalize expected result: %w", err)