New: a new interpretor based on Andrew Ng theory. (#3532)

### What problem does this PR solve?

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

agent/component/generate.py

@@ -124,11 +124,16 @@ class Generate(ComponentBase):
 
             cpn = self._canvas.get_component(component_id)["obj"]
             if cpn.component_name.lower() == "answer":
-                kwargs[para["key"]] = self._canvas.get_history(1)[0]["content"]
+                hist = self._canvas.get_history(1)
+                if hist:
+                    hist = hist[0]["content"]
+                else:
+                    hist = ""
+                kwargs[para["key"]] = hist
                 continue
             _, out = cpn.output(allow_partial=False)
             if "content" not in out.columns:
-                kwargs[para["key"]] = "Nothing"
+                kwargs[para["key"]] = ""
             else:
                 if cpn.component_name.lower() == "retrieval":
                     retrieval_res.append(out)