--- a/make/common/MakeBase.gmk	Wed Oct 17 21:51:00 2018 -0700
+++ b/make/common/MakeBase.gmk	Thu Oct 18 09:19:29 2018 +0200
@@ -656,8 +656,11 @@
 
 # String equals
 equals = \
-    $(and $(findstring $(strip $1),$(strip $2)),\
-        $(findstring $(strip $2),$(strip $1)))
+    $(if $(strip $1)$(strip $2),$(strip \
+      $(and $(findstring $(strip $1),$(strip $2)),\
+        $(findstring $(strip $2),$(strip $1)))), \
+      true \
+    )
 
 # Remove a whole list of prefixes
 # $1 - List of prefixes

--- a/test/make/TestMakeBase.gmk	Wed Oct 17 21:51:00 2018 -0700
+++ b/test/make/TestMakeBase.gmk	Thu Oct 18 09:19:29 2018 +0200
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2014, 2017, Oracle and/or its affiliates. All rights reserved.
+# Copyright (c) 2014, 2018, Oracle and/or its affiliates. All rights reserved.
 # DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 #
 # This code is free software; you can redistribute it and/or modify it
@@ -93,6 +93,7 @@
 
 EQUALS_VALUE1 := value1$(SPACE)
 EQUALS_VALUE2 := value2
+EQUALS_EMPTY :=
 
 ifneq ($(call equals, $(EQUALS_VALUE1), $(EQUALS_VALUE2)), )
   $(error The strings >$(EQUALS_VALUE1)< and >$(EQUALS_VALUE2)< are equal)
@@ -102,6 +103,18 @@
   $(error The strings >$(EQUALS_VALUE1)< and >$(EQUALS_VALUE1)< are not equal)
 endif
 
+ifeq ($(call equals, $(EQUALS_EMPTY), $(EQUALS_EMPTY)), )
+  $(error The strings >$(EQUALS_EMPTY)< and >$(EQUALS_EMPTY)< are not equal)
+endif
+
+ifneq ($(call equals, $(EQUALS_EMPTY), $(EQUALS_VALUE2)), )
+  $(error The strings >$(EQUALS_EMPTY)< and >$(EQUALS_VALUE2)< are equal)
+endif
+
+ifneq ($(call equals, $(EQUALS_VALUE2), $(EQUALS_EMPTY)), )
+  $(error The strings >$(EQUALS_VALUE2)< and >$(EQUALS_EMPTY)< are equal)
+endif
+
 ################################################################################
 # Test remove-prefixes