Address parse errors while using getVar to calculate dependency information

classes/rust.bbclass

@@ -7,7 +7,7 @@ def rust_base_dep(d):
     # Taken from meta/classes/base.bbclass `base_dep_prepend` and modified to
     # use rust instead of gcc
     deps = ""
-    if not d.getVar('INHIBIT_DEFAULT_RUST_DEPS'):
+    if not d.getVar('INHIBIT_DEFAULT_RUST_DEPS', True):
         if (d.getVar('HOST_SYS', True) != d.getVar('BUILD_SYS', True)):
             deps += " virtual/${TARGET_PREFIX}rust"
         else: