java_sdk_library: construct droidstubs args as []string

Bug: 145998881
Test: m checkbuild
Change-Id: Id3eb99577200a807050dbf86f47816a2476c3d9c
diff --git a/java/sdk_library.go b/java/sdk_library.go
index 4067bd3..a26474f 100644
--- a/java/sdk_library.go
+++ b/java/sdk_library.go
@@ -531,21 +531,36 @@
 	props.Merge_annotations_dirs = module.sdkLibraryProperties.Merge_annotations_dirs
 	props.Merge_inclusion_annotations_dirs = module.sdkLibraryProperties.Merge_inclusion_annotations_dirs
 
-	droiddocArgs := " --stub-packages " + strings.Join(module.sdkLibraryProperties.Api_packages, ":") +
-		" " + android.JoinWithPrefix(module.sdkLibraryProperties.Hidden_api_packages, " --hide-package ") +
-		" " + android.JoinWithPrefix(module.sdkLibraryProperties.Droiddoc_options, " ") +
-		" --hide MissingPermission --hide BroadcastBehavior " +
-		"--hide HiddenSuperclass --hide DeprecationMismatch --hide UnavailableSymbol " +
-		"--hide SdkConstant --hide HiddenTypeParameter --hide Todo --hide Typo"
+	droiddocArgs := []string{}
+	if len(module.sdkLibraryProperties.Api_packages) != 0 {
+		droiddocArgs = append(droiddocArgs, "--stub-packages "+strings.Join(module.sdkLibraryProperties.Api_packages, ":"))
+	}
+	if len(module.sdkLibraryProperties.Hidden_api_packages) != 0 {
+		droiddocArgs = append(droiddocArgs,
+			android.JoinWithPrefix(module.sdkLibraryProperties.Hidden_api_packages, " --hide-package "))
+	}
+	droiddocArgs = append(droiddocArgs, module.sdkLibraryProperties.Droiddoc_options...)
+	disabledWarnings := []string{
+		"MissingPermission",
+		"BroadcastBehavior",
+		"HiddenSuperclass",
+		"DeprecationMismatch",
+		"UnavailableSymbol",
+		"SdkConstant",
+		"HiddenTypeParameter",
+		"Todo",
+		"Typo",
+	}
+	droiddocArgs = append(droiddocArgs, android.JoinWithPrefix(disabledWarnings, "--hide "))
 
 	switch apiScope {
 	case apiScopeSystem:
-		droiddocArgs = droiddocArgs + " -showAnnotation android.annotation.SystemApi"
+		droiddocArgs = append(droiddocArgs, "-showAnnotation android.annotation.SystemApi")
 	case apiScopeTest:
-		droiddocArgs = droiddocArgs + " -showAnnotation android.annotation.TestApi"
+		droiddocArgs = append(droiddocArgs, " -showAnnotation android.annotation.TestApi")
 	}
 	props.Arg_files = module.sdkLibraryProperties.Droiddoc_option_files
-	props.Args = proptools.StringPtr(droiddocArgs)
+	props.Args = proptools.StringPtr(strings.Join(droiddocArgs, " "))
 
 	// List of APIs identified from the provided source files are created. They are later
 	// compared against to the not-yet-released (a.k.a current) list of APIs and to the