A developer needs to set a default value if a particular element in Process Data does not exist.
Given the following bpml code, what is the correct corresponding rule?

A.
<rule name=”IsFileSizeNotSet?”>
<condition>FileSize = 0</condition>
</rule>

B.
<rule name=”IsFileSizeNotSet?”>
<condition>FileSize.length() = 0</condition>
</rule>

C.
<rule name=”IsFileSizeNotSet?”>
<condition>string(/ProcessData/FileSize) = 0</condition>
</rule>

D.
<rule name=”IsFileSizeNotSet?”>
<condition>string-length(/ProcessData/FileSize) = 0</condition>
</rule>

Explanation: