fix: Update setStringValue method to handle null values by removing the key from context

src/main/java/de/extio/lmlib/agent/AgentContext.java

@@ -89,8 +89,12 @@ public final class AgentContext {
 	}
 	
 	public void setStringValue(final String key, final String value) {
+		if (value == null) {
+			this.context.remove(key);
+		} else {
 			this.context.put(key, List.of(value));
 		}
+	}
 	
 	public List<String> getStringValues(final String key) {
 		final var values = this.context.get(key);