Your ResourceLocation should be something like this:
private static final ResourceLocation TEXTURE = new ResourceLocation(YOUR_MOD_ID + ":textures/gui/some_gui.png");
Your ResourceLocation looks like this:
ResourceLocation texture = new ResourceLocation(Reference.MOD_ID,"/textures/gui/moduleListGUI.png");
1. Notice the colon (shouldn't be needed if you are using the 2 parameter constructor though).
2. You are adding an extra slash.
(The resource location should be toString to "modid:textures/gui/blah.png")