Compiler error

Hi, I have a static method

public class PolygonEditor {
  public static void create(PropertyInspector inspector) {

    PropertyInspector.PropertyRollup rollup = inspector.createRollup("PolygonEditor");

    rollup.addButton("switch water on selected", () -> {
       Logger.log("string");
    });
  }

}

It compiles and works.

But when I do this :

if (false) rollup.addButton("switch water on selected", () -> {
  Logger.log("string");
});

I'm getting the following error, what can it be ?

[INFO] Caused by: java.lang.NullPointerException  [INFO] 	at com.google.gwt.dev.jjs.impl.Pruner.transformToNullMethodCall(Pruner.java:608)  [INFO] 	at com.google.gwt.dev.jjs.impl.Pruner$CleanupRefsVisitor.endVisit(Pruner.java:184)  [INFO] 	at com.google.gwt.dev.jjs.ast.JMethodCall.traverse(JMethodCall.java:268)  [INFO] 	at com.google.gwt.dev.jjs.ast.JModVisitor.traverse(JModVisitor.java:361)  [INFO] 	at com.google.gwt.dev.jjs.ast.JModVisitor.accept(JModVisitor.java:273)  [INFO] 	... 32 more  [INFO]          [ERROR] at PolygonEditor.java(53): PolygonEditor.lambda$3()  [INFO]             com.google.gwt.dev.jjs.ast.JMethodCall  [INFO]          [ERROR] at PolygonEditor.java(53): PolygonEditor.lambda$3()  [INFO]             com.google.gwt.dev.jjs.ast.JExpressionStatement  [INFO]          [ERROR] at PolygonEditor.java(53): {  [INFO]   PolygonEditor.lambda$3();  [INFO] }  [INFO]             com.google.gwt.dev.jjs.ast.JBlock  [INFO]          [ERROR] at PolygonEditor.java(53): {  [INFO]   PolygonEditor.lambda$3();  [INFO] }  [INFO]             com.google.gwt.dev.jjs.ast.JMethodBody  [INFO]          [ERROR] at PolygonEditor.java(53): delightex.client.editors.PolygonEditor$lambda$3$Type.run()V  [INFO]             com.google.gwt.dev.jjs.ast.JMethod  [INFO]          [ERROR] at PolygonEditor.java(53): delightex.client.editors.PolygonEditor$lambda$3$Type (final extends Object implements Runnable)  [INFO]             com.google.gwt.dev.jjs.ast.JClassType  [INFO]       [ERROR] Unrecoverable exception, shutting down

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