This comes up every time I destroy a Graffiti block.
java.lang.IllegalArgumentException: Cannot get property DirectionProperty{name=facing, clazz=class net.minecraft.util.Direction, values=[north, east, south, west, up, down]} as it does not exist in Block{minecraft:air}
at net.minecraft.state.StateHolder.func_177229_b(SourceFile:93) ~[?:?] {re:classloading}
at com.silvaniastudios.graffiti.client.GraffitiRenderer.render(GraffitiRenderer.java:42) ~[?:1.0] {re:classloading}
at com.silvaniastudios.graffiti.client.GraffitiRenderer.func_225616_a_(GraffitiRenderer.java:20) ~[?:1.0] {re:classloading}
at net.minecraft.client.renderer.tileentity.TileEntityRendererDispatcher.func_228855_a_(TileEntityRendererDispatcher.java:137) ~[?:?] {re:classloading,pl:accesstransformer:B,xf:OptiFine:default}
at net.minecraft.client.renderer.tileentity.TileEntityRendererDispatcher.lambda$renderTileEntity$0(TileEntityRendererDispatcher.java:103) ~[?:?] {re:classloading,pl:accesstransformer:B,xf:OptiFine:default}
at net.minecraft.client.renderer.tileentity.TileEntityRendererDispatcher$$Lambda$11725/4669214.run(Unknown Source) ~[?:?] {}
at net.minecraft.client.renderer.tileentity.TileEntityRendererDispatcher.func_228853_a_(TileEntityRendererDispatcher.java:167) ~[?:?] {re:classloading,pl:accesstransformer:B,xf:OptiFine:default}
at net.minecraft.client.renderer.tileentity.TileEntityRendererDispatcher.func_228850_a_(TileEntityRendererDispatcher.java:97) ~[?:?] {re:classloading,pl:accesstransformer:B,xf:OptiFine:default}
at net.optifine.shaders.ShadersRender.renderShadowMap(ShadersRender.java:438) ~[?:?] {re:classloading}
at net.optifine.shaders.Shaders.beginRender(Shaders.java:4249) ~[?:?] {re:classloading}
at net.minecraft.client.renderer.GameRenderer.func_228378_a_(GameRenderer.java:926) ~[?:?] {re:classloading,pl:accesstransformer:B,xf:OptiFine:default}
at net.minecraft.client.renderer.GameRenderer.func_195458_a(GameRenderer.java:686) ~[?:?] {re:classloading,pl:accesstransformer:B,xf:OptiFine:default}
at net.minecraft.client.Minecraft.func_195542_b(Minecraft.java:924) [?:?] {re:classloading,pl:accesstransformer:B,pl:runtimedistcleaner:A}
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:553) [?:?] {re:classloading,pl:accesstransformer:B,pl:runtimedistcleaner:A}
at net.minecraft.client.main.Main.main(SourceFile:204) [?:?] {re:classloading}
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_51] {}
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_51] {}
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_51] {}
at java.lang.reflect.Method.invoke(Method.java:497) ~[?:1.8.0_51] {}
at net.minecraftforge.fml.loading.FMLClientLaunchProvider.lambda$launchService$0(FMLClientLaunchProvider.java:51) [forge-1.15.2-31.2.5.jar:31.2] {}
at net.minecraftforge.fml.loading.FMLClientLaunchProvider$$Lambda$433/979387846.call(Unknown Source) [forge-1.15.2-31.2.5.jar:31.2] {}
at cpw.mods.modlauncher.LaunchServiceHandlerDecorator.launch(LaunchServiceHandlerDecorator.java:37) [modlauncher-5.1.0.jar:?] {}
at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:54) [modlauncher-5.1.0.jar:?] {}
at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:72) [modlauncher-5.1.0.jar:?] {}
at cpw.mods.modlauncher.Launcher.run(Launcher.java:81) [modlauncher-5.1.0.jar:?] {re:classloading}
at cpw.mods.modlauncher.Launcher.main(Launcher.java:65) [modlauncher-5.1.0.jar:?] {re:classloading}

A detailed walkthrough of the error, its code path and all known details is as follows:

-- Head --
Thread: Render thread
Stacktrace:
at net.minecraft.state.StateHolder.func_177229_b(SourceFile:93)
at com.silvaniastudios.graffiti.client.GraffitiRenderer.render(GraffitiRenderer.java:42)
at com.silvaniastudios.graffiti.client.GraffitiRenderer.func_225616_a_(GraffitiRenderer.java:20)
at net.minecraft.client.renderer.tileentity.TileEntityRendererDispatcher.func_228855_a_(TileEntityRendererDispatcher.java:137)
at net.minecraft.client.renderer.tileentity.TileEntityRendererDispatcher.lambda$renderTileEntity$0(TileEntityRendererDispatcher.java:103)
at net.minecraft.client.renderer.tileentity.TileEntityRendererDispatcher$$Lambda$11725/4669214.run(Unknown Source)

-- Block Entity Details --
Details:
Name: graffiti:graffiti // com.silvaniastudios.graffiti.tileentity.TileEntityGraffiti
Block: Block{graffiti:graffiti}[facing=east]
Block location: World: (-1928,65,1800), Chunk: (at 8,4,8 in -121,112; contains blocks -1936,0,1792 to -1921,255,1807), Region: (-4,3; contains chunks -128,96 to -97,127, blocks -2048,0,1536 to -1537,255,2047)
Block: Block{minecraft:air}
Block location: World: (-1928,65,1800), Chunk: (at 8,4,8 in -121,112; contains blocks -1936,0,1792 to -1921,255,1807), Region: (-4,3; contains chunks -128,96 to -97,127, blocks -2048,0,1536 to -1537,255,2047)
Stacktrace:
at net.minecraft.client.renderer.tileentity.TileEntityRendererDispatcher.func_228853_a_(TileEntityRendererDispatcher.java:167)
at net.minecraft.client.renderer.tileentity.TileEntityRendererDispatcher.func_228850_a_(TileEntityRendererDispatcher.java:97)
at net.optifine.shaders.ShadersRender.renderShadowMap(ShadersRender.java:438)
at net.optifine.shaders.Shaders.beginRender(Shaders.java:4249)
at net.minecraft.client.renderer.GameRenderer.func_228378_a_(GameRenderer.java:926)