chore(concept): #578 create concept

docs/concept/#578-consistent-null-values/#578-consistent-null-values.md

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+# #578 Consistent null values
+
+| Key           | Value                                                                    |
+|---------------|--------------------------------------------------------------------------|
+| Author        | @ds-crehm                                                                |
+| Creation date | 28.02.2024                                                               |
+| Ticket Id     | [#578](https://github.com/eclipse-tractusx/traceability-foss/issues/578) |
+| State         | Draft                                                                    |
+
+# Table of Contents
+1. [Overview](#overview)
+2. [Requirements](#requirements)
+3. [Out of scope](#out-of-scope)
+4. [Concept](#concept)
+5. [References](#references)
+6. [Additional Details](#additional-details)
+
+
+# Overview
+In the frontend there are multiple versions of 'empty' values:
+![example-values-frontend.png](example-values-frontend.png)
+In the backend those values are as follows:
+![example-values-backend.png](example-values-backend.png)
+
+These should be consistent throughout Trace-X.
+
+# Requirements
+- Whenever a string value is saved or updated in the database and during data consumption from IRS:
+  - [ ] Leading and trailing whitespace characters are trimmed.
+  - [ ] Empty strings ("") are all converted to null.
+- [ ] Decision taken on *how* to show the values & all null values are shown accordingly in the frontend.
+- [ ] Leading and trailing whitespace characters don't count as mandatory values during user input.
+
+# Out of scope
+Any further string validation is out of scope. For example values like "-", "--", ".", "..." will not be changed and instead written into the database and shown in the frontend **unchanged**.
+
+# Concept
+### Backend
+Whenever a string is saved or updated in the database and during data consumption from IRS:
+1. Trim leading and whitespace character
+2. Convert empty strings ("") to null
+3. Save/update value in database
+
+### Frontend
+There are multiple options on how to show null values in the frontend.
+1. Empty
+![null-value-display-empty.png](null-value-display-empty.png)
+2. null
+![null-value-display-null.png](null-value-display-null.png)
+3. Placeholder character (for example "-") ideally in a different color
+![null-value-display-placeholder.png](null-value-display-placeholder.png)
+
+Once an option was chosen, the display of null values must be implemented accordingly.
+
+# References
+https://miro.com/app/board/uXjVO5JVoho=/?moveToWidget=3458764580844404410&cot=10
+
+# Additional Details
+Given the dynamic nature of ongoing development, there might be variations between the conceptualization and the current implementation. For the latest status, refer to the documentation.