Fix: Add error handling for missing 'tiles' key in stac_tile response

When TiTiler endpoint returns an error response (e.g., validation errors),
the response doesn't contain a 'tiles' key, causing a KeyError.

This fix:
- Checks if 'tiles' exists in the response before accessing it
- Provides informative error messages based on the API error response
- Handles both dict-based errors (with 'detail' key) and list-based
  validation errors
- Raises ValueError with descriptive message instead of bare KeyError

Fixes opengeos/geoai#468

Author: giswqs

leafmap/stac.py

@@ -850,6 +850,26 @@ def stac_tile(
                 titiler_endpoint.url_for_stac_item(), params=kwargs, timeout=10
             ).json()
 
+    # Check if the response contains tiles
+    if "tiles" not in r:
+        # Try to provide helpful error message from the API response
+        if "detail" in r:
+            error_msg = f"TiTiler endpoint error: {r['detail']}"
+        elif isinstance(r, list) and len(r) > 0:
+            # Handle validation errors (list of error dicts)
+            if isinstance(r[0], dict) and "msg" in r[0]:
+                errors = []
+                for e in r:
+                    loc = "->".join(str(x) for x in e.get("loc", []))
+                    msg = e.get("msg", "")
+                    errors.append(f"{loc}: {msg}")
+                error_msg = f"TiTiler endpoint validation failed: {'; '.join(errors)}"
+            else:
+                error_msg = f"TiTiler endpoint returned error list: {r}"
+        else:
+            error_msg = f"TiTiler endpoint returned unexpected response (missing 'tiles' key): {r}"
+        raise ValueError(error_msg)
+
     tiles = r["tiles"][0]
 
     # Convert 127.0.0.1 to localhost for Google Colab browser access