fix b4w real-world import

src/models/b4w.py

@@ -27,7 +27,7 @@ class B4wExport(ExportBaseModel):
     sign: Sign = Field(alias="CdtDbtInd")
     reference: str = Field(alias="RmtInf")
     other_name: str = Field(alias="RmtdNm")
-    other_iban: str = Field(alias="RmtdAcctIBAN", pattern=IBAN_PATTERN)
+    other_iban: str | None = Field(alias="RmtdAcctIBAN", pattern=IBAN_PATTERN)
     category: Category | None = Field(
         alias="Category",
         examples=[
@@ -51,7 +51,7 @@ class B4wExport(ExportBaseModel):
             "CdtDbtInd": f"{self.sign!s}",
             "RmtInf": f"{self.reference}",
             "RmtdNm": f"{self.other_name}",
-            "RmtdAcctIBAN": f"{self.other_iban}",
+            "RmtdAcctIBAN": f"{self.other_iban or ''}",
             "Category": f"{self.category.to_str() if self.category else ''}",
             "Notes": f"{self.notes}",
         }
@@ -77,6 +77,13 @@ class B4wExport(ExportBaseModel):
     def amount_signed(self) -> Decimal:
         return self.amount * self.sign.to_sign()
 
+    @field_validator("other_iban", mode="before")
+    @classmethod
+    def other_iban_blank_is_none(cls, iban_in: str | None) -> str | None:
+        if iban_in is None or (isinstance(iban_in, str) and not iban_in.strip()):
+            return None
+        return iban_in
+
     @field_validator("category", mode="before")
     @classmethod
     def category_str_is_parsable(