If you specifically have the Huawei (often internally codenamed or searched alongside "c7100"), the process differs slightly:
A "null IMEI" feels like a death sentence for a phone, but for MediaTek devices like the C7100, it is merely a software glitch. The process, while technical, has a high success rate when using the SN Write Tool with the correct database files.
If SN Writer fails with "S_DL_GET_DRAM_SETTING_FAIL," you need a scatter file. Use Miracle Box or UMtool instead.