E9 - Relational Operators

- Added missing-data handling for the relational operators <, <=, >
  and >=.

src/E9.cpp

@@ -289,6 +289,11 @@ void E9::operator_lt (Arg& result, Arg& left, Arg& right)
   }
   else if (left._type  == Arg::type_date ||
            right._type == Arg::type_date)
+  {
+    if (left._value == "" ||
+        right._value == "")
+      result._value = "false";
+    else
     {
       Date left_date  (left._value,  _dateformat);
       Date right_date (right._value, _dateformat);
@@ -297,6 +302,7 @@ void E9::operator_lt (Arg& result, Arg& left, Arg& right)
                     ? "true"
                     : "false";
     }
+  }
   else
   {
     result._value = (left._value < right._value)
@@ -322,6 +328,11 @@ void E9::operator_lte (Arg& result, Arg& left, Arg& right)
   }
   else if (left._type  == Arg::type_date ||
            right._type == Arg::type_date)
+  {
+    if (left._value == "" ||
+        right._value == "")
+      result._value = "false";
+    else
     {
       Date left_date  (left._value,  _dateformat);
       Date right_date (right._value, _dateformat);
@@ -330,6 +341,7 @@ void E9::operator_lte (Arg& result, Arg& left, Arg& right)
                     ? "true"
                     : "false";
     }
+  }
   else
   {
     result._value = (left._value <= right._value)
@@ -355,6 +367,11 @@ void E9::operator_gte (Arg& result, Arg& left, Arg& right)
   }
   else if (left._type  == Arg::type_date ||
            right._type == Arg::type_date)
+  {
+    if (left._value == "" ||
+        right._value == "")
+      result._value = "false";
+    else
     {
       Date left_date  (left._value,  _dateformat);
       Date right_date (right._value, _dateformat);
@@ -363,6 +380,7 @@ void E9::operator_gte (Arg& result, Arg& left, Arg& right)
                     ? "true"
                     : "false";
     }
+  }
   else
   {
     result._value = (left._value >= right._value)
@@ -387,6 +405,11 @@ void E9::operator_gt (Arg& result, Arg& left, Arg& right)
   }
   else if (left._type  == Arg::type_date ||
            right._type == Arg::type_date)
+  {
+    if (left._value == "" ||
+        right._value == "")
+      result._value = "false";
+    else
     {
       Date left_date  (left._value,  _dateformat);
       Date right_date (right._value, _dateformat);
@@ -395,6 +418,7 @@ void E9::operator_gt (Arg& result, Arg& left, Arg& right)
                                     ? "true"
                                     : "false";
     }
+  }
   else
   {
     result._value = (left._value > right._value)