conditionals: fix handling of empty string values

src/flb_conditionals.c

@@ -66,8 +66,14 @@ static struct flb_condition_rule *rule_create(const char *field,
     switch (op) {
     case FLB_RULE_OP_EQ:
     case FLB_RULE_OP_NEQ:
+        /* Allow empty string values for equality comparisons */
+        if (!value) {
+            return NULL;
+        }
+        break;
     case FLB_RULE_OP_REGEX:
     case FLB_RULE_OP_NOT_REGEX:
+        /* Regex patterns must not be empty */
         if (!value || !((char *)value)[0]) {
             return NULL;
         }

src/flb_processor.c

@@ -585,7 +585,12 @@ int flb_processor_unit_set_property(struct flb_processor_unit *pu, const char *k
 
     /* Handle the "condition" property for processor units */
     if (strcasecmp(k, "condition") == 0) {
-        return flb_processor_unit_set_condition(pu, v);
+        /* Only process if it's a structured map object */
+        if (v->type == CFL_VARIANT_KVLIST) {
+            return flb_processor_unit_set_condition(pu, v);
+        }
+        /* If string, ignore here - it will be handled by filter_modify */
+        return 0;
     }
 
     /* Handle normal properties */