Math operators incorrect when an argument is empty

[piotrszul]

For math operators if any of the argument is empty the result should be empty.

operator fails when right argument is empty - Math 6 exclusions

Details

No value present

• n1 * n4 [** Empty result multiplying empty collection (1)]
• n1 * i [** Empty result when one of the operands is null]
• n1 / i [** Empty result when one of the operands is null]
• n1 + i [** Empty result when one of the operands is null]
• n1 - i [** Empty result when one of the operands is null]
• n1 mod i [** Empty result when one of the operands is null]

'-' operator incorrect when right argument is empty - Math 6 exclusions

Details

No value present

• n1 - n4 [** Empty result when one of the operands is empty]

'+' should produce {} if any argument is empty - Math 6 exclusions

Details

Expected: null but got: one ==> expected: <null> but was: <one>

• s5 + n4 [** Empty result if one or both operands is empty (1b)]

[piotrszul]

It does work correctly for compatible numerical empty collections (e.g. empty Integer collection).
It fails with any empty collection of incompatible type including the empty collection literal which is the same as for 7.x.

[johngrimes]

On the v8 branch, when running the expression 5 * {}, I get:

au.csiro.pathling.errors.InvalidUserInputError: * operator does not support right operand: ??

[piotrszul]

@johngrimes How far do we want this to go? Should it be OK to call:
2 + true.where(false) and expect the result to be {} or should we still maintain some notion of the type of the computed empty collection?

[johngrimes]

Some test cases:

2 + true -> error
2 + active -> error
2 + true.where(%resource.active) -> error
2 + true.where(false) -> error
2 + true.where({}) -> error  // because of boolean evaluation of collections
2 + {} -> {}
2 + {}.where(true) -> {}
2 + foo -> {}
2 + true.where(1 = 2) -> error