bs/is: don't let an empty subreport disable the grand totals (fixes #588)

hledger/Hledger/Cli/CompoundBalanceCommand.hs

@@ -140,8 +140,14 @@ compoundBalanceCommand CompoundBalanceCommandSpec{..} CliOpts{command_=cmd, repo
                 row "Total" overalltotals'
               where
                 overalltotals = case subreporttotals of
-                  a1:as -> foldl' (zipWith (+)) a1 as
                   [] -> []
+                  ts -> foldl' (zipWith (+)) zeros ts'
+                    where
+                      -- A subreport might be empty and have no subtotals, count those as zeroes (#588).
+                      -- Varying-length subtotals rows are handled similarly, though that is not expected to happen.  
+                      len = maximum $ map length ts
+                      ts' = [take len $ as ++ repeat nullmixedamt | as <- ts]
+                      zeros = replicate len nullmixedamt
                 overalltotals'
                   | null overalltotals = []
                   | otherwise =  overalltotals

tests/balancesheet/balancesheet.test

@@ -174,3 +174,29 @@ Total:
 >>>2
 >>>=0
 
+# 8. An empty section is does not disrupt the overall totals, #588
+hledger -f- balancesheet -YTA
+<<<
+2017/1/1
+  (assets)  $1
+>>>
+Balance Sheet
+
+             ||  2017/12/31    Total  Average 
+=============++===============================
+ Assets      ||                               
+-------------++-------------------------------
+ assets      ||          $1       $1       $1 
+-------------++-------------------------------
+             ||          $1       $1       $1 
+=============++===============================
+ Liabilities ||                               
+-------------++-------------------------------
+-------------++-------------------------------
+             ||                               
+=============++===============================
+ Total       ||          $1       $1       $1 
+
+
+>>>2
+>>>=0

tests/balancesheet/pretty.test

@@ -20,7 +20,7 @@ Balance Sheet
 ─────────────╫─────────────
              ║             
 ═════════════╬═════════════
- Total       ║             
+ Total       ║           1 
 
 
 >>>2