It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import.
import crafttweaker.entity.AttributeModifier;

ZenGetter	GetterMethod	Return Type
ZenGetter uuid	GetterMethod getUUID()	Return Type string
ZenGetter nome	GetterMethod getName()	Return Type string
ZenGetter operation	GetterMethod getOperation()	Return Type int
ZenGetter amount	GetterMethod getAmount()	Return Type double
ZenGetter saved	GetterMethod isSaved()	Return Type boolean

SetterName	SetterMethod	Parameter Type
SetterName saved	SetterMethod setSaved(boolean)	Parameter Type boolean

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for operation:
0 = add: Increment X by Amount
1 = multiply_base: Increment Y by X * Amount
2 = multiply: Y = Y * (1 + Amount) (equivalent to Increment Y by Y * Amount).

ZenScript
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AttributeModifier.createModifier(String name, double amount, int operation, @Optional String uuid);