Use proptools.BoolDefault

Replace x == nil || *x with proptools.BoolDefault(x, true)

Test: m checkbuild
Change-Id: Icc5378cab3ea72d86544b40761c2f00b278cc0a1
diff --git a/java/java.go b/java/java.go
index fd0719c..a2eb810 100644
--- a/java/java.go
+++ b/java/java.go
@@ -1137,7 +1137,7 @@
 }
 
 func (j *Module) installable() bool {
-	return j.properties.Installable == nil || *j.properties.Installable
+	return BoolDefault(j.properties.Installable, true)
 }
 
 var _ Dependency = (*Library)(nil)
@@ -1231,7 +1231,7 @@
 
 func (j *Test) DepsMutator(ctx android.BottomUpMutatorContext) {
 	j.deps(ctx)
-	if j.testProperties.Junit == nil || *j.testProperties.Junit == true {
+	if BoolDefault(j.testProperties.Junit, true) {
 		ctx.AddDependency(ctx.Module(), staticLibTag, "junit")
 	}
 }
@@ -1460,5 +1460,6 @@
 }
 
 var Bool = proptools.Bool
+var BoolDefault = proptools.BoolDefault
 var String = proptools.String
 var inList = android.InList