3GPP 38.331: If absent, the UE applies the SCS as derived from the prach-ConfigurationIndex in RACH-ConfigGeneric (see tables Table 6.3.3.1-1, Table 6.3.3.1-2, Table 6.3.3.2-2 and Table 6.3.3.2-3, TS 38.211 [16]).

This procedure for msg1_SubcarrierSpacing NULL is not implemented, so we aplly the same value of UL SCS.