Cannot read property '1' of null

[beppino]

I’m trying to update my project (now in production) from GWT 2.8.2 GMD 2.3.0 to GWT 2.9.0 GMD 2.4.1.
At the very beginning of the application, maybe when it try to inject amCharts… but not sure, the Chrome console show this error:

TypeError: Cannot read property '1' of null at <anonymous>:19:431734 at Object.Nv8/ (<anonymous>:19:431738) at r (<anonymous>:19:440) at Object.0 (<anonymous>:19:11242) at r (<anonymous>:19:440) at <anonymous>:19:1440 at <anonymous>:19:1449 at $O_g$ (ScriptInjector.java:292) at jP_g$.kP_g$ [as inject_0_g$] (ScriptInjector.java:89) at W2g_g$ (GwtMaterialAmCore.java:49) at X2g_g$ (GwtMaterialAmCore.java:41) at V2g_g$.Y2g_g$ [as onModuleLoad_0_g$] (GwtMaterialAmCore.java:34) at Array.cVc_g$ (it_00046ftgm_00046hms_00046tin_00046AreaCritica__EntryMethodHolder.java:3) at initializeModules_0_g$ (ModuleUtils.java:44) at LQ_g$ (Impl.java:309) at OQ_g$ (Impl.java:368) at Impl.java:78 at wUc_g$ (ModuleUtils.java:55) at XPathPrefixResolver.java:24

Just for note, I’m not using maven (I can't). I’ve a lib folder with all the necessary jar.
Also, my project started in GMD 2.1.1 and migrated to 2.3.0 in developing. Other project, started directly from 2.3.0 passed to 2.4.1 are Ok! (?)