Type of term FilterRestrictions is defined as:
<ComplexType Name="FilterRestrictionsType">
<Property Name="Filterable" Type="Edm.Boolean" DefaultValue="true">
<Annotation Term="Core.Description" String="$filter is supported" />
</Property>
<Property Name="RequiresFilter" Type="Edm.Boolean" Nullable="true">
<Annotation Term="Core.Description" String="$filter is required" />
</Property>
<Property Name="RequiredProperties" Type="Collection(Edm.PropertyPath)">
<Annotation Term="Core.Description"
String="These properties must be specified in the $filter clause (properties of derived types are not allowed here)" />
</Property>
<Property Name="NonFilterableProperties" Type="Collection(Edm.PropertyPath)">
<Annotation Term="Core.Description" String="These properties cannot be used in $filter expressions" />
</Property>
</ComplexType>

The term lacks the intended default of "false" for property RequiresFilter. On the other hand, it has a Nullable="true" facet, which is the default anyway and can be omitted therefore.