in ecs-logging-core/src/main/java/co/elastic/logging/AdditionalField.java [56:62]
public static AdditionalField of(String additionalField) {
String[] keyValue = additionalField.split("=");
if (keyValue.length != 2) {
throw new IllegalArgumentException("Could not parse " + additionalField);
}
return new AdditionalField(keyValue[0].trim(), keyValue[1].trim());
}