Correct bug introduced in commit 63deaad. affecting Edit->Tax Report Options and the US Income Tax Report

Author: Alex Aycinena

libgnucash/engine/Account.cpp

@@ -4006,13 +4006,17 @@ gint64
 xaccAccountGetTaxUSCopyNumber (const Account *acc)
 {
     auto copy_number = get_kvp_int64_path (acc, {"tax-US", "copy-number"});
-    return copy_number ? *copy_number : 1;
+    return (copy_number && (*copy_number != 0)) ? *copy_number : 1;
 }
 
 void
 xaccAccountSetTaxUSCopyNumber (Account *acc, gint64 copy_number)
 {
-    set_kvp_int64_path (acc, {"tax-US", "copy-number"}, copy_number);
+    if (copy_number != 0)
+        set_kvp_int64_path (acc, {"tax-US", "copy-number"}, copy_number);
+    else
+        /* deletes KVP if it exists */
+        set_kvp_int64_path (acc, {"tax-US", "copy-number"}, std::nullopt);
 }
 
 /*********************************************************************\

libgnucash/engine/Account.h

@@ -1406,9 +1406,9 @@ typedef enum
     const char * xaccAccountGetTaxUSPayerNameSource (const Account *account);
     /** DOCUMENT ME! */
     void xaccAccountSetTaxUSPayerNameSource (Account *account, const char *source);
-    /** DOCUMENT ME! */
+    /** Returns copy_number stored in KVP; if KVP doesn't exist or copy_number is zero, returns 1 */
     gint64 xaccAccountGetTaxUSCopyNumber (const Account *account);
-    /** DOCUMENT ME! */
+    /** Saves copy_number in KVP if it is greater than 1; if copy_number is zero, deletes KVP */
     void xaccAccountSetTaxUSCopyNumber (Account *account, gint64 copy_number);
     /** @} */