binman: Generate an error when text is not provided

When the value of a text entry is not provided an execption is generated
talking about a None type. This is confusing. Add a more explanatory error
and a test for this case.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/binman/etype/text.py

@@ -51,6 +51,9 @@ class Entry_text(Entry):
         self.text_label, = self.GetEntryArgsOrProps(
             [EntryArg('text-label', str)])
         self.value, = self.GetEntryArgsOrProps([EntryArg(self.text_label, str)])
+        if not self.value:
+            self.Raise("No value provided for text label '%s'" %
+                       self.text_label)
 
     def ObtainContents(self):
         self.SetContents(self.value)

tools/binman/ftest.py

@@ -1369,6 +1369,13 @@ class TestFunctional(unittest.TestCase):
         data = self._DoReadFile('80_fill_empty.dts')
         self.assertEqual(chr(0) * 16, data)
 
+    def testTextMissing(self):
+        """Test for a text entry type where there is no text"""
+        with self.assertRaises(ValueError) as e:
+            self._DoReadFileDtb('66_text.dts',)
+        self.assertIn("Node '/binman/text': No value provided for text label "
+                      "'test-id'", str(e.exception))
+
 
 if __name__ == "__main__":
     unittest.main()