Function to convert a genotype in a GVCF file to a fasta sequence. All records must use non-symbloic alleles (except ), and duplicated positions are not allowed. Supports multisample VCFs. Parameters: gvcfFile: path to the GVCF file to use. The script accepts VCF file format, but GVCFs should be used to ensure that all variants are accounted for refFasta: path to the reference FASTA file outFile: path to the output FASTA file sampleName: optional, the sample name to use in a multisample VCF. Defaults to the first sample listed missingRecordAs: optional, default asRef. Behavior for positions that lack a GVCF record (variant site or ref block). Option asRef treats missing positions like reference blocks. Option asN fills the region with N's. Option asNone omits the region entirely. missingGenotypeAs: optional, default asN. Behavior for records with a missing or no-call genotype (.). Option asRef treats missing genotypes as reference alleles. Option asN fills missing genotypes with N. The number of N's is equal to the length of the record on the reference. Option asNone omits the position entirely. alleleIdx: optional. In a diploid or polyploid, the index of the allele to use. Defaults to 0.