1004 - Empty string not allowed for property '%s'.

Description
A property was defined as a string with an empty value in a context where a non-empty string is required.
Example
Config:
ObjectList( 'Obj' ) { .Compiler = '' // This should be a valid path }
Output:
c:\Test\fbuild.bff(1):(1) FASTBuild Error #1004 - ObjectList() - Empty string not allowed for property '.Compiler'. ObjectList( 'Obj' ) ^ \--here
Fix:
ObjectList( 'Obj' ) { .Compiler = 'MyCompiler' // A previously defined Compiler() }