remove unnecessary null check

Author: deleonenriqueta

logback13/src/main/java/com/newrelic/logging/logback13/NewRelicJsonLayout.java

@@ -74,9 +74,6 @@ private void writeToGenerator(ILoggingEvent eventObject, JsonGenerator generator
             String value;
 
             for (Map.Entry<String, String> entry : mdcPropertyMap.entrySet()) {
-                if (entry.getKey() == null || entry.getValue() == null) {
-                    continue;
-                }
                 key = entry.getKey();
                 value = entry.getValue();
                 generator.writeStringField(key, value);