`SPLIT` hangs on empty `delimiter`.

[python-processing-unit]

According to the specification section 9.1.5:

• TNS: SPLIT(STR: value, STR: delimiter = " ") = MUST split value on the exact substring delimiter and return the parts as a one-dimensional tensor of STR. delimiter MUST be non-empty. Consecutive delimiters and trailing delimiters MUST produce empty-string elements.

In the implementation, however, when an empty STR is passed to SPLIT as delimiter, the interpreter hangs, rather than erroring.