Errors when converting

[hauke96]

Raise errors, when something is not correct during parsing. Some situations where this might be useful:

Throwing error and exit program:

• duplicates in class/field names
• missing properties/name object
• incomplete property object (e.g. collection is missing)

Printing warning but still go on:

• unlikely property (e.g. empty name)
• additional and therefore unused stuff

Also put the line into the error-message