FIX: don't error when adding to canvas (#4055)

src/backend/base/langflow/components/prompts/LangChainHubPrompt.py

@@ -21,13 +21,14 @@ class LangChainHubPromptComponent(Component):
             name="langchain_api_key",
             display_name="Your LangChain API Key",
             info="The LangChain API Key to use.",
+            required=True,
         ),
         StrInput(
             name="langchain_hub_prompt",
             display_name="LangChain Hub Prompt",
-            info="The LangChain Hub prompt to use.",
-            value="efriis/my-first-prompt",
+            info="The LangChain Hub prompt to use, i.e., 'efriis/my-first-prompt'",
             refresh_button=True,
+            required=True,
         ),
     ]
 
@@ -36,7 +37,11 @@ class LangChainHubPromptComponent(Component):
     ]
 
     def update_build_config(self, build_config: dict, field_value: str, field_name: str | None = None):
-        if field_name == "langchain_hub_prompt":
+        # If the field is not langchain_hub_prompt or the value is empty, return the build config as is
+        if field_name != "langchain_hub_prompt" or not field_value:
+            return build_config
+
+        # Fetch the template
         template = self._fetch_langchain_hub_template()
 
         # Get the template's messages
@@ -84,6 +89,7 @@ class LangChainHubPromptComponent(Component):
                 info="Fill in the value for {" + custom_field + "}",
             ).to_dict()
 
+            # Add the new parameter to the build config
             build_config[f"param_{custom_field}"] = new_parameter
 
         return build_config
@@ -91,8 +97,10 @@ class LangChainHubPromptComponent(Component):
     async def build_prompt(
         self,
     ) -> Message:
-        # Get the parameters that
-        template = self._fetch_langchain_hub_template()  # TODO: doing this twice
+        # Fetch the template
+        template = self._fetch_langchain_hub_template()
+
+        # Get the parameters from the attributes
         original_params = {k[6:] if k.startswith("param_") else k: v for k, v in self._attributes.items()}
         prompt_value = template.invoke(original_params)
 
@@ -111,6 +119,7 @@ class LangChainHubPromptComponent(Component):
         # Check if the api key is provided
         if not self.langchain_api_key:
             msg = "Please provide a LangChain API Key"
+
             raise ValueError(msg)
 
         # Pull the prompt from LangChain Hub