U_BOOT_ARCH_PATCH_DIR should contain a value or should not be defined, empty string is not allowed

target/u-boot/Makefile.in

@@ -88,7 +88,7 @@ $(U_BOOT_DIR)/.patched: $(U_BOOT_DIR)/.unpacked
 	toolchain/patch-kernel.sh $(U_BOOT_DIR) target/u-boot/$(U_BOOT_VERSION) \
 		u-boot-$(U_BOOT_VERSION)-\*.patch \
 		u-boot-$(U_BOOT_VERSION)-\*.patch.$(ARCH)
-ifneq ($(strip $(U_BOOT_ARCH_PATCH_DIR)),"")
+ifneq ($(strip $(U_BOOT_ARCH_PATCH_DIR)),)
 	toolchain/patch-kernel.sh $(U_BOOT_DIR) $(U_BOOT_ARCH_PATCH_DIR) \*.patch
 endif
 ifneq ($(strip $(BR2_TARGET_UBOOT_CUSTOM_PATCH)),"")