diff --git a/gclc/src/main/java/net/bigeon/gclc/command/CommandParameters.java b/gclc/src/main/java/net/bigeon/gclc/command/CommandParameters.java
index 3a83d4f..c768837 100644
--- a/gclc/src/main/java/net/bigeon/gclc/command/CommandParameters.java
+++ b/gclc/src/main/java/net/bigeon/gclc/command/CommandParameters.java
@@ -207,7 +207,11 @@ public final class CommandParameters {
      * @param string the key
      * @param value the value */
     public void set(final String string, final String value) {
-        stringArguments.computeIfPresent(string,
-                (final String k, final String v) -> value);
+        // DO NOT USE computeIfPresent. This is a HashMap, not a ConcurrentHashMap and
+        // keys can be associated to null, but computeIfPresent will consider them as
+        // absent!
+        if (stringArguments.containsKey(string)) {
+            stringArguments.put(string, value);
+        }
     }
 }