// AddBlockHeader handles adding a block header to the store, through majority voting of observers
func (k msgServer) AddBlockHeader(goCtx context.Context, msg *types.MsgAddBlockHeader) (*types.MsgAddBlockHeaderResponse, error) {
	ctx := sdk.UnwrapSDKContext(goCtx)

	// check authorization for this chain
	chain := common.GetChainFromChainID(msg.ChainId)
+	if chain == nil {
+		return nil, types.ErrSupportedChains
+	}	
	if ok := k.IsAuthorized(ctx, msg.Creator, chain); !ok {
		return nil, types.ErrNotAuthorizedPolicy
	}
